Picture encoding device, picture encoding method, picture encoding program, picture decoding device, picture decoding method, and picture decoding program

ABSTRACT

A candidate list construction unit selects a plurality of blocks each having one or two pieces of motion information containing at least information about a motion vector and information about a reference picture from a plurality of neighboring encoded blocks of an encoding target block and constructs a candidate list containing candidates of the motion information used for the motion compensation prediction from the motion information of the selected blocks. A selected candidate generator generates a new candidate of the motion information by combining the motion information of a first prediction list derived by the first motion information deriving unit and the motion information of the second prediction list derived by a second motion information deriving unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/339,242, filed Oct. 31, 2016, which is a Continuation of U.S. patentapplication Ser. No. 14/109,629, filed Dec. 17, 2013, now U.S. Pat. No.9,516,314, which is a Continuation of PCT International Application No.PCT/JP2012/004148, filed Jun. 27, 2012, which claims the benefit ofJapanese Patent Application Nos. 2011-146065 and 2011-146066, filed Jun.30, 2011, and 2012-143340 and 2012-143341, filed Jun. 26, 2012.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a moving picture encoding technologyusing a motion compensation prediction, and in particular, relates to apicture encoding device, a picture encoding method, a picture encodingprogram, a picture decoding device, a picture decoding method, and apicture decoding program that encode or decode motion information usedfor a motion compensation prediction.

The motion compensation prediction is used in general moving picturecompression encoding. The motion compensation prediction is a technologythat partitions a target picture into fine blocks and uses a decodedpicture as a reference picture to generate a signal in a position movedfrom a target block of the target picture to a reference block of thereference picture as a prediction signal based on the amount of motionrepresented by a motion vector. The motion compensation prediction usesone motion vector to make a unidirectional prediction or uses two motionvectors to make a bidirectional prediction.

Regarding the motion vector, the compression efficiency is improved byselecting the motion vector of a neighboring encoded block of theprocessing target block as a motion vector predictor (also simply calleda vector predictor), determining a difference between the motion vectorof the processing target block and the vector predictor, andtransmitting the vector difference as a coding vector.

In MPEG-4AVC, the efficiency of the motion compensation prediction isimproved by making the block size of the motion compensation predictionfiner and more diverse than in MPEG-2. On the other hand, the number ofmotion vectors increases with a finer block size, posing a problem ofthe code amount of coding vectors.

Thus, while the motion vector of the left neighboring block is simplyselected as the vector predictor in MPEG-2, the precision of the vectorpredictor is improved and an increase of the code amount of codingvectors is inhibited in MPEG-4AVC by selecting a median of motionvectors of a plurality of neighboring blocks as the vector predictor.Further in MPEG-4AVC, a direct motion compensation prediction is known.The direct motion compensation prediction realizes a motion compensationprediction by generating a new motion vector by scaling the motionvector of the block located in the same position as the processingtarget block of another encoded picture based on distances between thetarget picture and two reference pictures without transmitting anycoding vector.

Also, a motion compensation prediction that realizes a motioncompensation prediction by using motion information of neighboringblocks of the processing target block without transmitting any codingvector is known (see, for example, Japanese Patent Application Laid-OpenPublication No. 10-276439).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open PublicationNo. 10-276439

As described above, the direct motion compensation prediction thattransmits no coding vector focuses on continuity of motion between theprocessing target block and the block located in the same position asthe processing target block of another encoded picture. In addition,Japanese Patent Application Laid-Open Publication No. 10-276439 focuseson continuity of motion between the processing target block and aneighboring block of the processing target block. Accordingly, theencoding efficiency is improved by not encoding motion informationcontaining a vector difference by using motion information of otherblocks.

According to the conventional motion compensation prediction, however,if the motion of the processing target block is shifted from the motionof a neighboring block of the processing target block or the motion of ablock located in the periphery of the same position as of the processingtarget block of another encoded picture, information containing a vectordifference needs to be encoded, posing a difficult aspect that theimprovement of encoding efficiency is not sufficiently achieved.

The present invention is made in view of such circumstances and anobject thereof is to provide a technology that further improves theencoding efficiency of motion information containing a motion vector.

SUMMARY OF THE INVENTION

To solve the above task, a picture encoding device according to anaspect of the present invention is a picture encoding device with amotion compensation prediction including a candidate list constructionunit configured to select a plurality of blocks each having one or twopieces of motion information containing at least information about amotion vector and information about a reference picture from a pluralityof neighboring encoded blocks of an encoding target block and toconstruct a candidate list containing candidates of the motioninformation used for the motion compensation prediction from the motioninformation of the selected blocks, a first motion information derivingunit configured to derive the motion information of a first predictionlist from a first candidate contained in the candidates, a second motioninformation deriving unit configured to derive the motion information ofa second prediction list from a second candidate contained in thecandidates, and a selected candidate generator configured to generate anew candidate of the motion information by combining the motioninformation of the first prediction list derived by the first motioninformation deriving unit and the motion information of the secondprediction list derived by the second motion information deriving unit.

When a number of the candidates does not reach a set maximum number, thecandidate list construction unit may construct a candidate listincluding a new candidate generated by the selected candidate generator.

The candidate list construction unit may construct the candidate listincluding at least the one candidate generated by the selected candidategenerator such that the number of the candidates does not exceed themaximum number.

A bitstream generator configured to encode candidate identificationinformation to identify the candidate of the motion information used forthe motion compensation prediction in the candidate list may further beincluded.

The candidate list construction unit may assign the candidateidentification information larger than that of the candidates to the newcandidate generated by the selected candidate generator.

The first prediction list and the second prediction list may bedifferent prediction lists.

The candidate list construction unit may include the motion informationderived from the motion information of the block of a picture temporallydifferent from the picture including the encoding target block in thecandidate list.

The first motion information deriving unit may search for the candidatesaccording to a first priority order for the candidate that becomes validto set the candidate as the first candidate. The second motioninformation deriving unit may search for the candidates according to asecond priority order for the candidate that becomes valid to set thecandidate as the second candidate.

The first motion information deriving unit may set a preset candidateamong the candidates as the first candidate. The second motioninformation deriving unit may set another preset candidate among thecandidates as the second candidate.

When both of the motion information of the first prediction list and themotion information of the second prediction list derived by the firstmotion information deriving unit and the second motion informationderiving unit respectively are valid, the selected candidate generatormay generate the new candidate.

The new candidate may hold two pieces of the motion information. The newcandidate may hold one piece of the motion information.

Another aspect of the present invention is a picture encoding method.The method is a picture encoding method with a motion compensationprediction including selecting a plurality of blocks each having one ortwo pieces of motion information containing at least information about amotion vector and information about a reference picture from a pluralityof neighboring encoded blocks of an encoding target block andconstructing a candidate list containing candidates of the motioninformation used for the motion compensation prediction from the motioninformation of the selected blocks, deriving the motion information of afirst prediction list from a first candidate contained in the candidatelist, deriving the motion information of a second prediction list from asecond candidate contained in the candidate list, and generating a newcandidate of the motion information by combining the motion informationof the first prediction list and the motion information of the secondprediction list.

A picture decoding device according to an aspect of the presentinvention is a picture decoding device with a motion compensationprediction including a candidate list construction unit configured toselect a plurality of blocks each having one or two pieces of motioninformation containing at least information about a motion vector andinformation about a reference picture from a plurality of neighboringdecoded blocks of a decoding target block and to construct a candidatelist containing candidates of the motion information used for the motioncompensation prediction from the motion information of the selectedblocks, a first motion information deriving unit configured to derivethe motion information of a first prediction list from a first candidatecontained in the candidates, a second motion information deriving unitconfigured to derive the motion information of a second prediction listfrom a second candidate contained in the candidates, and a selectedcandidate generator configured to generate a new candidate of the motioninformation by combining the motion information of the first predictionlist derived by the first motion information deriving unit and themotion information of the second prediction list derived by the secondmotion information deriving unit.

If a number of the candidates does not reach a set maximum number, thecandidate list construction unit may construct a candidate listincluding a new candidate generated by the selected candidate generator.

The candidate list construction unit may construct the candidate listincluding at least the one candidate generated by the selected candidategenerator such that the number of the candidates does not exceed themaximum number.

A bitstream analysis unit configured to decode candidate identificationinformation to identify the candidate of the motion information used forthe motion compensation prediction in the candidate list and a selectionunit configured to select one candidate from selection candidatescontained in the candidate list generated by the candidate listconstruction unit by using the decoded candidate identificationinformation may further be included.

The candidate list construction unit may assign the candidateidentification information larger than that of the candidates to the newcandidate generated by the selected candidate generator.

The first prediction list and the second prediction list may bedifferent prediction lists.

The candidate list construction unit may include the motion informationderived from the motion information of the block of a picture temporallydifferent from the picture including the decoding target block in thecandidate list.

The first motion information deriving unit may search for the candidatesaccording to a first priority order for the candidate that becomes validto set the candidate as the first candidate. The second motioninformation deriving unit may search for the candidate according to asecond priority order to set the candidate that becomes valid as thesecond candidate.

The first motion information deriving unit may set a preset candidateamong the candidates as the first candidate. The second motioninformation deriving unit may set another preset candidate among thecandidates as the second candidate.

If both of the motion information of the first prediction list and themotion information of the second prediction list derived by the firstmotion information deriving unit and the second motion informationderiving unit respectively are valid, the selected candidate generatormay generate the new candidate.

The new candidate may hold two pieces of motion information. The newcandidate may hold one piece of motion information.

Another aspect of the present invention is a picture decoding method.The method includes:

selecting a plurality of blocks each having one or two pieces of motioninformation containing at least information about a motion vector andinformation about a reference picture from a plurality of neighboringdecoded blocks of a decoding target block and constructing a candidatelist containing candidates of the motion information used for the motioncompensation prediction from the motion information of the selectedblocks, deriving the motion information of a first prediction list froma first candidate contained in the candidate list, deriving the motioninformation of a second prediction list from a second candidatecontained in the candidate list; and

generating a new candidate of the motion information by combining themotion information of the first prediction list and the motioninformation of the second prediction list.

Any combination of the above elements and what is converted of therepresentation of the present invention among the method, device,system, recording medium, and computer program are also valid as anaspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, byway of example only, with referenceto the accompanying drawings which are meant to be exemplary, notlimiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a diagram illustrating an example of partitioning a pictureinto maximum coding blocks;

FIGS. 2A and 2B are diagrams illustrating a coding block;

FIGS. 3A to 3D are diagrams illustrating a prediction block;

FIG. 4 is a diagram illustrating a prediction block size;

FIG. 5 is a diagram illustrating a prediction coding mode;

FIGS. 6A to 6D are diagrams illustrating a prediction direction of amotion compensation prediction;

FIG. 7 is a diagram illustrating an example of syntax of the predictionblock;

FIGS. 8A to 8C are diagrams illustrating a Truncated Unary bitstream ofa merge index;

FIG. 9 is a diagram illustrating a configuration of a moving pictureencoding device according to a first embodiment of the presentinvention;

FIG. 10 is a diagram illustrating a management method of motioninformation in a motion information memory in FIG. 9;

FIG. 11 is a diagram illustrating the configuration of a motioninformation generator in FIG. 9;

FIG. 12 is a diagram illustrating the configuration of a vectordifference calculation unit in FIG. 9;

FIG. 13 is a diagram illustrating a spatial candidate block group;

FIG. 14 is a diagram illustrating a temporal candidate block group;

FIG. 15 is a diagram illustrating the configuration of a combined motioninformation decision unit in FIG. 11;

FIG. 16 is a diagram illustrating the configuration of a combined motioninformation candidate generator in FIG. 15;

FIG. 17 is a diagram illustrating the configuration of a bidirectionalcombined motion information candidate list construction unit in FIG. 16;

FIG. 18 is a diagram illustrating a candidate number management table;

FIGS. 19A and 19B are diagrams illustrating conversion from a mergecandidate number into a merge index;

FIG. 20 is a flow chart illustrating an operation of encoding of themoving picture encoding device according to the first embodiment of thepresent invention;

FIG. 21 is a flow chart illustrating the operation of the motioninformation generator in FIG. 9;

FIG. 22 is a flow chart illustrating the operation of the vectordifference calculation unit in FIG. 11;

FIG. 23 is a flow chart illustrating the operation of the combinedmotion information decision unit in FIG. 11;

FIG. 24 is a flow chart illustrating the operation of the bidirectionalcombined motion information candidate list construction unit in FIG. 16;

FIG. 25 is a flow chart illustrating the operation of constructing aspatial combined motion information candidate list;

FIG. 26 is a flow chart illustrating the operation of constructing atemporal combined motion information candidate list;

FIG. 27 is a flow chart illustrating the operation of constructing abidirectional combined motion information candidate list;

FIG. 28 is a flow chart illustrating the operation of a referencedirection motion information decision unit in FIG. 17;

FIG. 29 is a flow chart illustrating the operation of a reversedirection motion information decision unit in FIG. 17;

FIG. 30 is a diagram illustrating a decision of the prediction directionof bidirectional combined motion information candidates;

FIGS. 31A to 31C are diagrams illustrating extension examples of thedecision of the prediction direction of bidirectional combined motioninformation candidates;

FIG. 32 is a diagram illustrating the configuration of a moving picturedecoding device according to the first embodiment of the presentinvention;

FIG. 33 is a diagram illustrating the configuration of a motioninformation reproducing unit in FIG. 32;

FIG. 34 is a diagram illustrating the configuration of a motion vectorreproducing unit in FIG. 33;

FIG. 35 is a diagram illustrating the configuration of a combined motioninformation reproducing unit in FIG. 33;

FIG. 36 is a flow chart illustrating the operation of decoding of themoving picture decoding device according to the first embodiment of thepresent invention;

FIG. 37 is a flow chart illustrating the operation of the motioninformation reproducing unit in FIG. 32;

FIG. 38 is a flow chart illustrating the operation of the motion vectorreproducing unit in FIG. 33;

FIG. 39 is a flow chart illustrating the operation of the combinedmotion information reproducing unit in FIG. 33;

FIGS. 40A and 40B are diagrams illustrating candidate number managementtables according to a first modification;

FIG. 41 is a diagram illustrating another candidate number managementtable according to the first modification of the first embodiment;

FIG. 42 is a flow chart illustrating derivation of a bidirectionalcombined motion information candidate (BD2);

FIG. 43 is a flow chart illustrating derivation of a bidirectionalcombined motion information candidate (BD3);

FIG. 44 is a flow chart illustrating the operation of a reversedirection motion information decision unit according to a secondmodification of the first embodiment;

FIG. 45 is a flow chart illustrating the operation of a reversedirection motion information decision unit according to a thirdmodification of the first embodiment;

FIG. 46 is a flow chart illustrating the configuration of a combinedmotion information candidate generator according to a fourthmodification of the first embodiment;

FIG. 47 is a diagram illustrating the operation of a reference directionmotion information decision unit and the operation of a reversedirection motion information decision unit according to the fourthmodification of the first embodiment;

FIG. 48 is a diagram illustrating combinations of motion information inwhich two prediction directions according to a fifth modification of thefirst embodiment are the same;

FIGS. 49A and 49B are diagrams illustrating preset combinations of BD0and BD1 according to a sixth modification of the first embodiment;

FIG. 50 is a diagram (part 1) illustrating an effect of the firstembodiment;

FIG. 51 is a diagram (part 2) illustrating the effect of the firstembodiment;

FIG. 52 is a diagram (part 3) illustrating the effect of the firstembodiment;

FIGS. 53A and 53B are diagrams illustrating syntax that encodes acandidate number management table according to a second embodiment in abitstream;

FIG. 54 is a diagram illustrating a candidate number management tableaccording to a third embodiment;

FIG. 55 is a diagram illustrating the configuration of a combined motioninformation candidate generator according to the third embodiment;

FIG. 56 is a flow chart illustrating the configuration of the combinedmotion information candidate generator according to the thirdembodiment;

FIG. 57 is a flow chart illustrating the operation of a candidate numbermanagement table changing unit according to the third embodiment;

FIGS. 58A to 58C are diagrams illustrating change examples of thecandidate number management table of the candidate number managementtable changing unit according to the third embodiment;

FIG. 59 is a flow chart illustrating the operation of a candidate numbermanagement table changing unit according to a first modification of thethird embodiment;

FIGS. 60A and 60B are diagrams illustrating the candidate numbermanagement tables of the candidate number management table changing unitaccording to the first modification of the third embodiment;

FIG. 61 is a flow chart illustrating the operation of a candidate numbermanagement table changing unit according to a second modification of thethird embodiment;

FIG. 62 is a flow chart illustrating the operation of a candidate numbermanagement table changing unit according to a third modification of thethird embodiment;

FIG. 63 is a flow chart illustrating the operation of a referencedirection motion information decision unit according to a fourthembodiment;

FIG. 64 is a diagram illustrating the configuration of a combined motioninformation candidate generator according to a fifth embodiment;

FIG. 65 is a diagram illustrating a candidate number management tableaccording to a sixth embodiment;

FIG. 66 is a flow chart illustrating the configuration of a referencedirection decision unit according to the sixth embodiment; and

FIG. 67 is a flowchart illustrating a calculation technique of motionvectors mvL0t, mvL1t of temporal combined motion information candidates.

DETAILED DESCRIPTION OF THE INVENTION

First, technologies assumed for the embodiments of the present inventionwill be described.

Currently, devices and systems conforming to encoding schemes such asMPEG (Moving Picture Experts Group) are widely used. In such encodingschemes, a sequence of a plurality of pictures on a time base is handledas information of a digital signal. For the purpose of broadcasting,transmitting, or accumulating highly efficient information, compressionencoding is performed by using the motion compensation prediction usingredundancy in the time direction and orthogonal transformation such as adiscrete cosine transform using redundancy in the space direction.

In 1995, the MPEG-2 video (ISO/IEC 13818-2) encoding scheme was drawn upas a general video compression encoding scheme and has been widely usedfor accumulation media such as DVD and magnetic tape of digital VTRconforming to the D-VHS (registered trademark) standard and applicationsof digital broadcasting and the like.

Further, in 2003, the encoding scheme called MPEG-4 AVC/H.264 (thestandard number of 14496-10 is given in ISO/IEC and H.264 in ITU-T.Hereinafter, the encoding scheme will be called MPEG-4AVC) was drawn upas an international standard by cooperative work between the jointtechnical committee (ISO/IEC) of the ISO (International StandardsOrganization) and IEC (International Electrotechnical Commission) andITU-T (International Telecommunication Union-Telecommunication Sector).

Currently, standardization of the encoding scheme called HEVC is underway by cooperative work between the joint technical committee (ISO/IEC)of the ISO (International Standards Organization) and IEC (InternationalElectrotechnical Commission) and ITU-T (International TelecommunicationUnion-Telecommunication Sector).

(Coding Block)

In the embodiments of the present invention, an input picture signal ispartitioned into maximum coding block units as shown in FIG. 1 and thepartitioned coding blocks are processed in a raster-scan order. Thecoding block has a hierarchical structure and can be partitioned intosmaller coding blocks by successive equal quadrisection in considerationof the encoding efficiency and the like. Coding blocks obtained byquadrisection are encoded in a zigzag scan order. The coding block thatcan no longer partitioned is called the minimum coding block. The codingblock becomes the unit of encoding and the maximum coding block alsobecomes a coding block when the number of partitions is 0. In thepresent embodiment, it is assumed that the maximum coding block is 64pixels×64 pixels and the minimum coding block is 8 pixels×8 pixels.

FIGS. 2A and 2B show examples of partition of the maximum coding block.In the example of FIG. 2A, the coding block is partitioned into 10coding blocks. CU0, CU1, and CU9 are coding blocks of 32 pixels×32pixels, CU2, CU3, and CU8 are coding blocks of 16 pixels×16 pixels, andCU4, CU5, CU6, and CU7 are coding blocks of 8 pixels×8 pixels.

(Prediction Block)

In the embodiments of the present invention, a coding block is furtherpartitioned into prediction blocks. FIGS. 3A to 3D show patterns ofpartition of the prediction block. FIG. 3A shows 2N×2N that does notpartition the coding block, FIG. 3B shows 2N×N that horizontallypartitions the coding block, FIG. 3C shows N×2N that verticallypartitions the coding block, and FIG. 3D shows N×N that horizontally andvertically partitions the coding block. That is, as shown in FIG. 4, 13prediction block sizes ranging from the 64 pixels×64 pixels as themaximum prediction block size for which the number of CU partitions is 0to 4 pixels×4 pixels as the minimum prediction block size for which thenumber of CU partitions is 3.

In the present embodiment, the maximum coding block is set to 64pixels×64 pixels and the minimum coding block is set to 8 pixels×8pixels, but the embodiments are not limited to such combinations. Also,patterns of partition of prediction blocks are set as shown in FIGS. 3Ato 3D, but the coding block only needs to be partitioned into oneprediction block or more and patterns are not limited to the abovepatterns.

(Prediction Coding Mode)

In the embodiments of the present invention, the prediction direction ofthe motion compensation prediction or the number of coding vectors canbe switched by the block size of the prediction block. An example of theprediction coding mode associating the prediction direction of themotion compensation prediction and the number of coding vectors willbriefly be described using FIG. 5.

The prediction coding mode shown in FIG. 5 include a unidirectional mode(UniPred) in which the prediction direction of the motion compensationprediction is unidirectional and the number of coding vectors is 1, abidirectional mode (BiPred) in which the prediction direction of themotion compensation prediction is bidirectional and the number of codingvectors is 2, and a merge mode (MERGE) in which the prediction directionof the motion compensation prediction is unidirectional or bidirectionaland the number of coding vectors is 0. In addition, an intra mode(Intra) which is a prediction coding mode that not perform a motioncompensation prediction is provided.

(Reference Picture Index)

In the embodiments of the present invention, the optimum referencepicture can be selected from a plurality of reference pictures in amotion compensation prediction to improve the precision of the motioncompensation prediction. Thus, the reference picture used for a motioncompensation prediction is encoded in a bitstream as a reference pictureindex together with a coding vector. The reference picture index usedfor the motion compensation prediction is a numerical value larger thanor equal to 0. A plurality of reference images selected by the referencepicture index is managed by a reference index list. If the predictiondirection of the compensation prediction is unidirectional, onereference picture index is encoded and if the prediction direction ofthe compensation prediction is bidirectional, a reference picture indexindicating a reference picture of each of the prediction directions isencoded (see FIG. 5).

(Vector Predictor Index)

In HEVC, selecting the optimum vector predictor from a plurality ofvector predictor candidates to improve the precision of the vectorpredictor and encoding a vector predictor index to indicate the selectedvector predictor are under discussion. In the embodiments of the presentinvention, the above vector predictor index is introduced. If theprediction direction of the compensation prediction is unidirectional,one vector predictor index is encoded and if the prediction direction ofthe compensation prediction is bidirectional, a vector predictor indexindicating a vector predictor of each of the prediction directions isencoded (see FIG. 5).

(Merge Index)

In HEVC, selecting the optimum block from blocks located in the samepositions as a plurality of neighboring block candidates and processingtarget blocks of other encoded pictures and encoding and decoding amerge index indicating the selected block to further improve theencoding efficiency are under discussion. This is a motion compensationprediction technology (merge technology) to use motion informationcomprising the prediction direction of the motion compensationprediction of the selected block indicated by the merge index, motionvector information, and reference picture information for the processingtarget block. In the embodiments of the present invention, the abovemerge index (merger technology) is introduced. As shown in FIG. 5, onemerge index is encoded when the prediction coding mode is the mergemode. If the motion information is bidirectional, the motion informationcontains motion vector information and reference picture information ofeach prediction direction.

Hereinafter, motion information possessed by a block that may beindicated by a merge index will be called a combined motion informationcandidate and an aggregate of combined motion information candidateswill be called a combined motion information candidate list.

(Prediction Direction)

In the embodiments of the present invention, two directions, an L0direction and an L1 direction, are set as the prediction direction ofthe motion compensation prediction. The prediction direction of themotion compensation prediction will briefly be described using FIGS. 6Ato 6D. When the prediction direction of the motion compensationprediction is unidirectional, one of the L0 direction and the L1direction is used. FIG. 6A shows a case when the prediction direction ofthe motion compensation prediction is unidirectional and a referencepicture (RefL0Pic) in the L0 direction is a time prior to a codingtarget picture (CurPic). FIG. 6B shows a case when the predictiondirection of the motion compensation prediction is unidirectional andthe reference picture in the L0 direction is a time subsequent to thecoding target picture. The reference picture in the L0 direction inFIGS. 6A and 6B can be replaced by a reference picture (RefL1Pic) in theL1 direction.

When the prediction direction of the motion compensation prediction isbidirectional, both of the L0 direction and the L1 direction are usedare represented as a BI direction. FIG. 6C shows a case when theprediction direction of the motion compensation prediction isbidirectional and the reference picture in the L0 direction is a timeprior to the coding target picture and the reference picture in the L1direction is a time subsequent to the coding target picture. FIG. 6Dshows a case when the prediction direction of the motion compensationprediction is bidirectional and the reference picture in the L0direction and the reference picture in the L1 direction are times priorto the coding target picture. The reference picture in the L0 directionin FIGS. 6C and 6D can be replaced by the reference picture (RefL1Pic)in the L1 direction and the reference picture in the L1 direction can bereplaced by the reference picture in the L0 direction. As has beendescribed above, the L0 direction and the L1 direction as the predictiondirections of the motion compensation prediction can each be representedas temporally forward or backward. A plurality of reference pictures canbe present in each of the L0 direction and the L1 direction andreference pictures are determined after reference pictures in the L0direction are added to a reference picture list L0, reference picturesin the L1 direction are added to a reference picture list L1, and theposition of the reference picture in the reference picture list isspecified by the reference picture index in each prediction direction.Hereinafter, that the prediction direction is the L0 direction meansthat motion information associated with reference pictures added to thereference picture list L0 is used in the prediction direction and thatthe prediction direction is the L1 direction means that motioninformation associated with reference pictures added to the referencepicture list L1 is used in the prediction direction.

(Syntax)

An example of syntax of a prediction block according to an embodiment ofthe present invention will be described using FIG. 7. Whether aprediction block is intra or inter is specified by an upper coding blockand FIG. 7 shows syntax when the prediction block is inter. In aprediction block, a merge flag (merge_flag), a merge index (merge_idx),a motion compensation prediction direction (inter_pred_type), referenceindexes (ref_idx_l0 and ref_idx_l1), vector differences (mvd_l0[0],mvd_l0[1], mvd_l1[0], mvd_l1[1]), and vector predictor indexes(mvp_idx_l0 and mvp_idx_l1) are set up. [0] of a vector differenceindicates a horizontal component and [1] indicates a vertical component.

ref_idx_l0, mvd_l0[0], mvd_l0[1], and mvp_idx_l0 are information relatedto the L0 direction and ref_idx_l1, mvd_l1[0], mvd_l1[1], and mvp_idx_l1are information related to the L1 direction. inter_pred_type includesthree types of Pred_L0 (unidirectional in the L0 direction), Pred_L1(unidirectional in the L1 direction), and Pred_BI (bidirectional in BI).

(Code Amount of Motion Information)

As is evident from the syntax in FIG. 7, the merge mode can transmitmotion information using one merge index. Thus, if a prediction error ofthe merge mode (with the merge flag set to 1) and that of the non-mergemode (with the merge flag set to 0) are comparable, the merge mode canencode motion information more efficiently. That is, the encodingefficiency of motion information can be improved by increasing theselection rate of the merge mode.

While the syntax of a prediction block according to an embodiment of thepresent invention is set as shown in FIG. 7, the merge mode only needsto be able to encode motion information with less information thannon-merge modes according to an embodiment of the present invention andthus, the syntax is not limited to the above example. For example,motion information may include only a vector difference.

(Properties of the Merge Index)

In FIG. 7, NumMergeCands( ) as a function to calculate the number ofmerge candidates is set up before decoding (encoding) of merge indexesand NumMergeCands( ) as a function to calculate the number of vectorpredictor candidates is set up before decoding (encoding) of vectorpredictor indexes. These functions are needed to derive the numbers ofcandidates because the number of merge candidates and the number ofvector predictor candidates change from prediction block to predictionblock based on validity of motion information of neighboring blocks.That motion information of a neighboring block is valid means that theneighboring block is not a block outside the region and is not in intramode and that motion information of a neighboring block is invalid meansthat the neighboring block is a block outside the region and is in intramode.

If the number of merge candidates is 1, the merge index is not decoded(encoded). This is because if the number of merge candidates is 1, thecandidate can uniquely be decided without being specified. This alsoapplies to the vector predictor index.

The bitstring of a merge index will be described using FIGS. 8A to 8C.In the embodiments of the present invention, a Truncated Unary bitstringwill be used as a merge index bitstring. FIG. 8A shows a merge indexbitstring using the Truncated Unary bitstring when the number of mergecandidates is 2, FIG. 8B shows a merge index bitstring using theTruncated Unary bitstring when the number of merge candidates is 3, andFIG. 8C shows a merge index bitstring using the Truncated Unarybitstring when the number of merge candidates is 4.

It is evident from FIGS. 8A to 8C that even if the same merge indexvalue is encoded, the number of code bits assigned to the merge indexdecreases with a decreasing number of merge candidates. When, forexample, the merge index is 1, while the number of bits is 1 with ‘1’ ifthe number of merge candidates is 2, the number of bits is 2 with ‘10’if the number of merge candidates is 3.

As described above, the encoding efficiency of merge index improves witha decreasing number of merge candidates. That is, the encodingefficiency can be improved by eliminating candidates of a low selectionrate while retaining candidates of a high selection rate. If the numbersof candidates are the same, a smaller merge index has a smaller codeamount and thus, the encoding efficiency can be improved by assigning asmaller merge index to a candidate of a high selection rate.

(POC)

In the embodiments of the present invention, POC (Picture Order Count)is used as time information (distance information) of pictures. POC is acounter defined in MPEG-4AVC and indicating the display order ofpictures. If the display order of pictures increases by 1, POC alsoincreases by 1. Thus, a time difference (distance) between pictures canbe derived from a POC difference between pictures.

(Properties of Motion Information of Neighboring Blocks)

In general, a correlation between motion information of the processingtarget block and motion information of a neighboring block of theprocessing target block (hereinafter, called a neighboring block)becomes high when the processing target block and the neighboring blockmakes the same motion, for example, when a region including theprocessing target block and the neighboring block is being translated.Also in general, a correlation between motion information of theprocessing target block and motion information of the neighboring blockdepends on the length in contact between the processing target block andthe neighboring block.

(Properties of Motion Information of Other Pictures)

On the other hand, a correlation between a block in the same position asthe processing target block in another decoded picture (hereinafter,called the same position block) used in time direct mode or space directmode in general and the processing target block becomes high when thesame position block and the processing target block are in a restingstate.

Hereinafter, preferred embodiments of the moving picture encodingdevice, moving picture encoding method, and moving picture encodingprogram according to the present invention will be described in detailtogether with drawings. The same reference signs are attached to thesame elements in the description of drawings to omit a duplicatedescription.

First Embodiment

(Configuration of a Moving Picture Encoding Device 100)

FIG. 9 shows the configuration of the moving picture encoding device 100according to the first embodiment of the present invention. The movingpicture encoding device 100 is a device that encodes a moving picturesignal in prediction block units in which a motion compensationprediction is performed. It is assumed that the partition of the codingblock, the decision of the prediction block size, and the decision ofthe prediction coding mode are decided by an upper coding controller.

The moving picture encoding device 100 is realized by hardware such asan information processing apparatus including a CPU (Central ProcessingUnit), frame memory, and hard disk. The moving picture encoding device100 realizes functional elements described below with the above elementsoperating. The position information of the prediction block to beprocessed, the prediction block size, and the prediction direction ofmotion compensation prediction are assumed to be shared inside themoving picture encoding device 100 and are not illustrated.

The moving picture encoding device 100 according to the first embodimentincludes a prediction block picture deriving unit 101, a subtractionunit 102, a prediction error encoder 103, a bitstream generator 104, aprediction error decoder 105, a motion compensation unit 106, anaddition unit 107, a motion vector detection unit 108, a motioninformation generator 109, a frame memory 110, and a motion informationmemory 111.

(Function of the Moving Picture Encoding Device 100)

The function of each unit will be described below. The prediction blockpicture deriving unit 101 derives a picture signal of the predictionblock to be processed from a picture signal supplied from a terminal 10based on the position information of the prediction block and theprediction block size and supplies the picture signal of the predictionblock to the subtraction unit 102, the motion vector detection unit 108,and the motion information generator 109.

The subtraction unit 102 calculates a prediction error signal bysubtracting a picture signal supplied by the prediction block picturederiving unit 101 from a prediction signal supplied by the motioncompensation unit 106 and supplies the prediction error signal to theprediction error encoder 103.

The prediction error encoder 103 generates prediction error coding databy performing processing such as quantization and orthogonaltransformation on a prediction error signal supplied by the subtractionunit 102 and supplies the prediction error coding data to the bitstreamgenerator 104 and the prediction error decoder 105.

The bitstream generator 104 generates a bitstream by entropy-encodingprediction error coding data supplied by the prediction error encoder103 and the merge flag, merge candidate number, prediction direction ofa motion compensation prediction, reference picture index, vectordifference, and vector index supplied by the motion informationgenerator 109 together with the prediction direction of the motioncompensation prediction according to the syntax and supplies thebitstream to a terminal 11.

Here, the merge candidate number is converted into a merge index togenerate a bitstream. The merge candidate number is the numberindicating the selected combined motion information candidate. Theconversion of the merge candidate number into a merge index will bedescribed later. In the first embodiment, as described above, theTruncated Unary bitstream is used to encode the merge index and thevector predictor index, but the present embodiment is not limited to theTruncated Unary bitstream if a bitstream is capable of encoding using adecreasing number of bits with a decreasing number of candidates.

The prediction error decoder 105 generates a prediction error signal byperforming processing such as inverse quantization and inverseorthogonal transformation on prediction error coding data supplied bythe prediction error encoder 103 and supplies the prediction errorsignal to the addition unit 107.

The motion compensation unit 106 generates a prediction signal by makingmotion compensation for a reference picture in the frame memory 110indicated by the reference picture index supplied by the motioninformation generator 109 based on a motion vector supplied by themotion information generator 109. If the prediction direction isbidirectional, an average of prediction signals in the L0 direction andthe L1 direction is set as a prediction signal.

The addition unit 107 generates a decoded picture signal by adding aprediction error signal supplied by the prediction error decoder 105 anda prediction signal supplied by the motion compensation unit 106 andsupplies the decoded picture signal to the frame memory 110.

The motion vector detection unit 108 detects a motion vector and areference picture index indicating a reference picture from a picturesignal supplied by the prediction block picture deriving unit 101 and apicture signal corresponding to a plurality of reference pictures andsupplies the motion vector and the reference picture index to the motioninformation generator 109. If the prediction direction is bidirectional,motion vectors and reference picture indexes in the L0 direction and theL1 direction are detected.

In a general detection method of a motion vector, an error evaluationvalue is calculated for a picture signal corresponding to a referencepicture moved by a predetermined amount of movement from the sameposition of a picture signal of a target picture and the amount ofmovement that minimizes the error evaluation value is set as the motionvector. As the error evaluation value, SAD (Sum of Absolute Difference)showing a sum of absolute differences or MSE (Mean Square Error) showinga mean square error can be used.

The motion information generator 109 generates a merge candidate number,or a vector difference and a vector predictor index from a motion vectorand a reference picture index supplied by the motion vector detectionunit 108, a candidate block group supplied by the motion informationmemory 111, and a reference picture indicated by a reference pictureindex in the frame memory 110 and supplies the merge flag, mergecandidate number, reference picture index, vector difference, or vectorpredictor index to the bitstream generator 104, the motion compensationunit 106, and the motion information memory 111 when necessary. Adetailed configuration of the motion information generator 109 will bedescribed later.

The frame memory 110 stores a decoded picture signal supplied by theaddition unit 107. In addition, as many decoded pictures whose decodingof the whole picture is completed as a predetermined number larger thanor equal to 1 are stored as reference pictures. The frame memory 110supplies a stored reference picture signal to the motion compensationunit 106 and the motion information generator 109. A storage area tostore reference pictures is controlled by the FIFO (First In First Out)method.

The motion information memory 111 stores motion information supplied bythe motion information generator 109 as a predetermined number ofpictures in minimum prediction block size units. Motion information ofneighboring blocks of the block to be processed is set as a spatialcandidate block group.

In addition, the motion information memory 111 sets the block on ColPicin the same position as the prediction block to be processed andneighboring blocks thereof are set as a temporal candidate block group.The motion information memory 111 supplies the spatial candidate blockgroup and the temporal candidate block group to the motion informationgenerator 109 as a candidate block group. The motion information memory111 is synchronized with the frame memory 110 and is controlled by theFIFO (First In First Out) method.

ColPic is refers to a decoded picture separate from the prediction blockto be processed and a picture stored in the frame memory 110 as areference picture. In the first embodiment, ColPic is assumed to be thereference picture decoded immediately before. ColPic is assumed to bethe reference picture decoded immediately before in the firstembodiment, but ColPic only needs to be an encoded picture and may be,for example, the reference picture immediately before in the displayorder or immediately after in the display order and can also bespecified in a bitstream.

The management method of motion information in the motion informationmemory 111 will be described using FIG. 10. The motion information isstored in each memory area in minimum prediction block units. FIG. 10shows a state when the prediction block size to be processes is 16pixels×16 pixels. In this case, motion information of the predictionblock is stored in 16 shaded memory areas in FIG. 10.

When the prediction coding mode is the intra mode, (0, 0) is stored as amotion vector in the L0 direction and the L1 direction and “−1” isstored as a reference picture index in the L0 direction and the L1direction. “−1” of the reference picture index may be any value allowingone to determine to be a mode in which no motion compensation predictionis performed. Hereinafter, if not specifically mentioned, a block simplyexpressed as such is assumed to indicate the minimum prediction blockunit. When the block is a block outside the region, like when the modeis the intra mode, (0, 0) is stored as a motion vector in the L0direction and the L1 direction and “−1” is stored as a reference pictureindex in the L0 direction and the L1 direction. That the LX direction (Xis 0 or 1) is valid means that the reference picture index in the LXdirection is larger than or equal to 0 and that the LX direction (X is 0or 1) is invalid (not valid) means that the reference picture index inthe LX direction is “−1”.

Subsequently, a detailed configuration of the motion informationgenerator 109 will be described using FIG. 11. FIG. 11 shows theconfiguration of the motion information generator 109. The motioninformation generator 109 includes a vector difference calculation unit120, a combined motion information decision unit 121, and a predictioncoding mode decision unit 122. A terminal 12 is connected to the motioninformation memory 111, a terminal 13 is connected to the motion vectordetection unit 108, a terminal 14 is connected to the frame memory 110,a terminal 15 is connected to the prediction block picture deriving unit101, a terminal 16 is connected to the bitstream generator 104, aterminal 50 is connected to the motion compensation unit 106, and aterminal 51 is connected to the motion information memory 111.

The function of each unit will be described below. The vector differencecalculation unit 120 decides a vector predictor index from a candidateblock group supplied from the terminal 12, a motion vector and areference picture index supplied from the terminal 13, a referencepicture supplied from the terminal 14, and a picture signal suppliedfrom the terminal 15 to calculate a vector difference and a ratedistortion evaluation value. Then, the vector difference calculationunit supplies the reference picture index, the motion vector, the vectordifference, the vector predictor index, and the rate distortionevaluation value to the prediction coding mode decision unit 122. Adetailed configuration of the vector difference calculation unit 120will be described later.

The combined motion information decision unit 121 constructs a combinedmotion information candidate list from the candidate block groupsupplied from the terminal 12, the reference picture supplied from theterminal 14, and the picture signal supplied from the terminal 15. Then,the combined motion information decision unit 121 selects a combinedmotion information candidate from the constructed combined motioninformation candidate list and decides its merge candidate number andalso calculates a rate distortion evaluation value before supplyingmotion information, the merge candidate number, and the rate distortionevaluation value of the combined motion information candidate to theprediction coding mode decision unit 122. A detailed configuration ofthe combined motion information decision unit 121 will be describedlater.

The prediction coding mode decision unit 122 compares the ratedistortion evaluation value supplied by the vector differencecalculation unit 120 and the rate distortion evaluation value suppliedby the combined motion information decision unit 121. If the former isless than the latter, the merge flag is set to “0”. The predictioncoding mode decision unit 122 supplies the merge flag and the referencepicture index, vector difference, and vector predictor index supplied bythe vector difference calculation unit 120 to the terminal 16 andsupplies the motion vector and reference picture index supplied by thevector difference calculation unit 120 to the terminal 50.

If the former is larger than or equal to the latter, the merge flag isset to 1. The prediction coding mode decision unit 122 supplies themerge flag and the merge candidate number supplied by the combinedmotion information decision unit 121 to the terminal 16 and supplies themotion vector of motion information and reference picture index suppliedby the combined motion information decision unit 121 to the terminal 50and the terminal 51. While details of a concrete calculation method of arate distortion evaluation value are not a principal objective of thepresent invention and so are omitted, the rate distortion evaluationvalue is an evaluation value having a property that the encodingefficiency increases with a decreasing rate distortion evaluation value.

Subsequently, a detailed configuration of the vector differencecalculation unit 120 will be described using FIG. 12. FIG. 12 shows theconfiguration of the vector difference calculation unit 120. The vectordifference calculation unit 120 includes a vector predictor candidatelist construction unit 130, a vector predictor decision unit 131, and asubtraction unit 132. A terminal 17 is connected to the predictioncoding mode decision unit 122.

The vector predictor candidate list construction unit 130 is similarlyset up in a moving picture decoding device 200 that decodes a bitstreamgenerated by the moving picture encoding device 100 according to thefirst embodiment to construct a vector predictor candidate list that isconsistent in the moving picture encoding device 100 and the movingpicture decoding device 200.

The function of each unit will be described below. The vector predictorcandidate list construction unit 130 deletes candidates blocks outsidethe region and candidates blocks whose mode is the intra mode from thecandidate block group supplied from the terminal 12. Further, if aplurality of candidate blocks having duplicate motion vectors ispresent, the vector predictor candidate list construction unit 130retains one candidate block and deletes other candidate blocks. Thevector predictor candidate list construction unit 130 constructs avector predictor candidate list from candidate blocks after the deletionand supplies the vector predictor candidate list to the vector predictordecision unit 131. The vector predictor candidate list constructed asdescribed above contains one vector predictor candidate or more withoutduplication. When, for example, there is no candidate block having amotion vector, a vector (0, 0) is added to the vector predictorcandidate list. If the prediction direction is bidirectional, a vectorpredictor candidate list is generated and supplied for the L0 directionand the L1 direction.

The vector predictor decision unit 131 selects the optimum vectorpredictor to the motion vector supplied from the terminal 13 from thevector predictor candidate list supplied by the vector predictorcandidate list construction unit 130. The vector predictor decision unit131 supplies the selected vector predictor to the subtraction unit 132and also supplies a reference picture index and a vector predictor indexas information indicating the selected vector predictor to the terminal17. If the prediction direction is bidirectional, the optimum vectorpredictor is selected and supplied for the L0 direction and the L1direction.

As the optimum vector predictor, a prediction error amount is calculatedfrom a reference picture supplied from the terminal 14 and a picturesignal supplied from the terminal 15 based on a motion vector possessedby the vector predictor candidate. Then, a rate distortion evaluationvalue is calculated from code amounts of a reference picture index,vector difference, and vector predictor index and the above predictionerror amount and the vector predictor candidate that minimizes the ratedistortion evaluation value is selected.

The subtraction unit 132 calculates a vector difference by subtractingthe vector predictor supplied by the vector predictor decision unit 131from the motion vector supplied from the terminal 13 and supplies thevector difference to the terminal 17. If the prediction direction isbidirectional, a vector difference is calculated and supplied for the L0direction and the L1 direction.

(Candidate Block Group Supplied to the Vector Predictor Candidate ListConstruction Unit 130)

A candidate block group supplied to the vector predictor candidate listconstruction unit 130 will be described using FIGS. 13 and 14. Acandidate block group contains a spatial candidate block group and atemporal candidate block group.

FIG. 13 shows neighboring blocks of the prediction block to be processedwhen the prediction block size to be processed is 16 pixels×16 pixels.In the first embodiment, the spatial candidate block group is assumed toinclude five blocks of a block A1, a block C, a block D, a block B1, anda block E shown in FIG. 13. It is assumed here that the spatialcandidate block group includes five blocks of the block A1, the block C,the block D, the block B1, and the block E, but the spatial candidateblock group only needs to include at least one neighboring processedblock of the prediction block to be processed and is not limited to theabove example. For example, all of the block A1, a block A2, a block A3,a block A4, the block B1, a block B2, a block B3, a block B4, the blockC, the block D, and the block E may be set as spatial candidate blocks.

Next, a temporal candidate block group will be described using FIG. 14.FIG. 14 shows blocks in the prediction block on ColPic in the sameposition as the prediction block to be processed and neighboring blocksthereof. In the first embodiment, the temporal candidate block groupincludes two blocks of a block H and a block I6 shown in FIG. 6.

It is assumed here that the temporal candidate block group is assumed toinclude two blocks of the block H and the block I6 on ColPic, but thetemporal candidate block group only needs to be at least one block on adecoded picture other than the prediction block to be processed and isnot limited to the above example. For example, all of a block I1 to ablock I16, a block A to a block A4, a block B1 to a block B4, a block C,a block D, a block E, a block F1 to a block F4, a block G1 to a blockG4, and the block H on ColPic may be set as temporal candidate blocks.Hereinafter, if not specifically mentioned, the block A4 is written asthe block A and the block B4 is written as the block B. Hereinafter, ifnot specifically mentioned, blocks of the block H and the block I6 arewritten as temporal blocks.

(Configuration of the Combined Motion Information Decision Unit 121)

Subsequently, a detailed configuration of the combined motioninformation decision unit 121 will be described using FIG. 15. FIG. 15shows the configuration of the combined motion information decision unit121. The combined motion information decision unit 121 includes acombined motion information candidate generator 140 and a combinedmotion information selection unit 141. The combined motion informationcandidate generator 140 is similarly set up in the moving picturedecoding device 200 that decodes a bitstream generated by the movingpicture encoding device 100 according to the first embodiment toconstruct a combined motion information list that is consistent andidentical in the moving picture encoding device 100 and the movingpicture decoding device 200.

The function of each unit will be described below. The combined motioninformation candidate generator 140 constructs a combined motioninformation candidate list from a candidate block group supplied fromthe terminal 12 and supplies the combined motion information candidatelist to the combined motion information selection unit 141. A detailedconfiguration of the combined motion information candidate generator 140will be described later.

The combined motion information selection unit 141 selects the optimumcombined motion information candidate from the combined motioninformation candidate list supplied by the combined motion informationcandidate generator 140 and supplies the merge candidate number asinformation indicating the selected combined motion informationcandidate to the terminal 17.

As the optimum combined motion information candidate, a prediction erroramount is calculated from a reference picture obtained based on theprediction direction, motion vector, and reference picture index of thecombined motion information candidate and supplied from the terminal 14and a picture signal supplied from the terminal 15. A rate distortionevaluation value is calculated from the code amount of the mergecandidate number and the prediction error amount to select the combinedmotion information candidate that minimizes the rate distortionevaluation value.

(Candidate Block Group Supplied to the Combined Motion InformationCandidate Generator 140)

The candidate block group supplied to the combined motion informationcandidate generator 140 will be described using FIGS. 13 and 14. Acandidate block group contains a spatial candidate block group and atemporal candidate block group. In the first embodiment, the spatialcandidate block group is assumed to include four blocks of the block A4,the block B4, the block C, and the block E shown in FIG. 13. It isassumed here that the spatial candidate block group includes four blocksof the block A4, the block B4, the block C, and the block E, but thespatial candidate block group only needs to include at least oneneighboring processed block of the prediction block to be processed andis not limited to the above example.

Next, the temporal candidate block group will be described using FIG.14. In the first embodiment, the temporal candidate block group includestwo blocks of the block H and the block I6 shown in FIG. 14. It isassumed here that the temporal candidate block group is the same as thetemporal candidate block group supplied to the vector predictorcandidate list construction unit 130, but the temporal candidate blockgroup only needs to be at least a block larger than or equal to 0 on adecoded picture other than the prediction block to be processed and isnot limited to the above example.

(Configuration of the Combined Motion Information Candidate Generator140)

Subsequently, a detailed configuration of the combined motioninformation candidate generator 140 featuring the first embodiment willbe described using FIG. 16. FIG. 16 shows the configuration of thecombined motion information candidate generator 140. A terminal 18 isconnected to the combined motion information selection unit 141. Thecombined motion information candidate generator 140 includes aunidirectional combined motion information candidate list constructionunit 150, a first combined motion information candidate list deletionunit 151, a bidirectional combined motion information candidate listconstruction unit 152, and a second combined motion informationcandidate list deletion unit 153.

The function of each unit will be described below. The unidirectionalcombined motion information candidate list construction unit 150constructs a first combined motion information candidate list from acandidate block group supplied from the terminal 12 and supplies thefirst combined motion information candidate list to the first combinedmotion information candidate list deletion unit 151.

If a plurality of combined motion information candidates havingduplicate motion information is present in the first combined motioninformation candidate list supplied by the unidirectional combinedmotion information candidate list construction unit 150, the firstcombined motion information candidate list deletion unit 151 constructsa second combined motion information candidate list by retaining onecombined motion information candidate while deleting other combinedmotion information candidates before supplying the second combinedmotion information candidate list to the bidirectional combined motioninformation candidate list construction unit 152.

The bidirectional combined motion information candidate listconstruction unit 152 constructs a bidirectional combined motioninformation candidate list from the second combined motion informationcandidate list supplied by the first combined motion informationcandidate list deletion unit 151 and generates a third combined motioninformation candidate list by combining the bidirectional combinedmotion information candidate list with the second combined motioninformation candidate list before supplying the third combined motioninformation candidate list to the second combined motion informationcandidate list deletion unit 153. A detailed configuration of thebidirectional combined motion information candidate list constructionunit 152 will be described later.

In the first embodiment, the bidirectional combined motion informationcandidate list construction unit 152 is assumed to construct abidirectional combined motion information candidate (BD0) whosereference direction is L0 and a bidirectional combined motioninformation candidate (BD1) whose reference direction is L1. Thus, theabove bidirectional combined motion information candidate list maycontain BD0 and BD1.

If a plurality of combined motion information candidates havingduplicate motion information is present in the third combined motioninformation candidate list supplied by the bidirectional combined motioninformation candidate list construction unit 152, the second combinedmotion information candidate list deletion unit 153 constructs acombined motion information candidate list by retaining one combinedmotion information candidate while deleting other combined motioninformation candidates before supplying the combined motion informationcandidate list to the terminal 18.

The unidirectional combined motion information candidate is a motioninformation candidate of a candidate block used by the so-called mergetechnology and motion information obtained from one candidate block. Onthe other hand, the bidirectional combined motion information is afeature technology of the first embodiment and is motion informationobtained by using two pieces of motion information of two candidateblocks. In the present embodiment, as two pieces of motion information,one piece of motion information in the L0 direction and one piece ofmotion information in the L1 direction are used.

(Bidirectional Combined Motion Information Candidate List ConstructionUnit 152)

Subsequently, a detailed configuration of the bidirectional combinedmotion information candidate list construction unit 152 will bedescribed using FIG. 17. FIG. 17 shows the configuration of thebidirectional combined motion information candidate list constructionunit 152. A terminal 19 is connected to the first combined motioninformation candidate list deletion unit 151 and a terminal 20 isconnected to the second combined motion information candidate listdeletion unit 153. The bidirectional combined motion informationcandidate list construction unit 152 includes a reference directiondecision unit 160, a reference direction motion information decisionunit 161, a reverse direction motion information decision unit 162, anda bidirectional motion information decision unit 163.

The function of each unit will be described below. The referencedirection decision unit 160 decides a reference direction of abidirectional combined motion information candidate from a secondcombined motion information candidate list and sends the referencedirection and the second combined motion information candidate listsupplied from the terminal 19 to the reference direction motioninformation decision unit 161. The reference direction for thebidirectional combined motion information candidate (BD0) whosereference direction is L0 is the L0 direction and the referencedirection for the bidirectional combined motion information candidate(BD1) whose reference direction is L1 is the L1 direction.

The reference direction motion information decision unit 161 decides amotion vector and a reference picture index in the reference directionof a bidirectional combined motion information candidate from thereference direction and the second combined motion information candidatelist supplied by the reference direction decision unit 160 and sends thereference direction, the motion vector and the reference picture indexin the reference direction, and the second combined motion informationcandidate list to the reverse direction motion information decision unit162.

The reverse direction motion information decision unit 162 decides amotion vector and a reference picture index in the reverse direction ofthe bidirectional combined motion information candidate from thereference direction, the motion vector and the reference picture indexin the reference direction, and the second combined motion informationcandidate list supplied by the reference direction motion informationdecision unit 161. The reverse direction motion information decisionunit 162 sends the motion vector and the reference picture index in thereference direction, the motion vector and the reference picture indexin the reverse direction, and the second combined motion candidate listto the bidirectional motion information decision unit 163. In the firstembodiment, if the reference direction is the L0 direction, the reversedirection is set to the L1 direction and if the reference direction isthe L1 direction, the reverse direction is set to the L0 direction.

The bidirectional motion information decision unit 163 decides abidirectional combined motion information candidate from the motionvector and the reference picture index in the reference direction andthe motion vector and the reference picture index in the reversedirection supplied by the reverse direction motion information decisionunit 162. The bidirectional motion information decision unit 163 alsoconstructs a third combined motion information candidate list from thesecond combined motion information candidate list and sends the thirdcombined motion information candidate list to the terminal 20.

(Candidate Number Management Table)

A candidate number management table showing the relationship between themerge candidate number used in the first embodiment and a combinedmotion information candidate will be described using FIG. 18. The mergecandidate numbers 0 to 6 indicate a combined motion informationcandidate (A) of the block A contained in the combined motioninformation candidate list, a combined motion information candidate (B)of the block B, a combined motion information candidate (COL) of atemporal block, a combined motion information candidate (C) of the blockC, a combined motion information candidate (E) of the block E, thebidirectional combined motion information candidate (BD0) whosereference direction is L0, and the bidirectional combined motioninformation candidate (BD1) whose reference direction is L1respectively. The maximum number of combined motion informationcandidates contained in the combined motion information candidate listis assumed to be 7 (the maximum number of merge indexes is 6). As shownabove, the merge candidate numbers of the bidirectional combined motioninformation candidate (BD0) whose reference direction is L0 and thebidirectional combined motion information candidate (BD1) whosereference direction is L1 are assigned so as to be larger than the mergecandidate numbers of unidirectional combined motion informationcandidates. The candidate number management table used in the firstembodiment is assumed to be the one shown in FIG. 18, but the table isonly required that a decreasing merge candidate number should beassigned to a combined motion information candidate with an increasingselection rate and the present embodiment is not limited to the abovetable.

The maximum number of combined motion information candidates containedin the candidate number management table and the combined motioninformation candidate list is assumed to be shared in the moving pictureencoding device 100 and is not illustrated. Hereinafter, the conversionfrom the merge candidate number into a merge index will be describedusing FIGS. 19A and 19B.

FIG. 19A shows that the merge candidate number directly becomes themerge index when a combined motion information candidate of the block A,a combined motion information candidate of the block B, a combinedmotion information candidate of the temporal block, a combined motioninformation candidate of the block C, a combined motion informationcandidate of the block E, a bidirectional combined motion informationcandidate whose reference direction is L0, and a bidirectional combinedmotion information candidate whose reference direction is L1 are allvalid.

FIG. 19B shows a case in which when combined motion informationcandidates contain invalid blocks, the merge index is assigned inascending order of merge candidate number by skipping invalid mergecandidate numbers. If, as shown in FIG. 19B, combined motion informationcandidates of the block B whose merge candidate number is 1 and theblock E whose merge candidate number is 4 are invalid, the merge index 0is converted into the merge candidate number 0, the merge index 1 isconverted into the merge candidate number 2, the merge index 2 isconverted into the merge candidate number 3, the merge index 3 isconverted into the merge candidate number 5, and the merge index 4 isconverted into the merge candidate number 6. As shown above, the mergeindexes of the bidirectional combined motion information candidate (BD0)whose reference direction is L0 and the bidirectional combined motioninformation candidate (BD1) whose reference direction is L1 are assignedso as to be larger than the merge indexes of unidirectional combinedmotion information candidates.

In the moving picture decoding device 200 that decodes a bitstreamgenerated by the moving picture encoding device 100 according to thefirst embodiment, a reverse conversion from the merge index into themerge candidate number is performed to generate the consistent andidentical candidate number management table in the moving pictureencoding device 100 and the moving picture decoding device 200.

(Operation of the Moving Picture Encoding Device 100)

Subsequently, the operation of encoding by the moving picture encodingdevice 100 according to the first embodiment will be described using theflow chart in FIG. 20. The prediction block picture deriving unit 101derives a picture signal of the prediction block to be processed from apicture signal supplied from the terminal 10 based on positioninformation of the prediction block and the prediction block size(S100).

The motion vector detection unit 108 detects a motion vector and areference picture index indicating a reference picture from the picturesignal supplied by the prediction block picture deriving unit 101 and apicture signal corresponding to a plurality of reference pictures(S101).

The motion information generator 109 generates a merge candidate number,or a vector difference and a vector predictor index from the motionvector and reference picture index supplied from the motion vectordetection unit 108 and a candidate block group supplied by the motioninformation memory 111 (S102).

The motion compensation unit 106 generates a prediction signal by makingmotion compensation for the reference picture in the frame memory 110indicated by the reference picture index based on the motion vectorsupplied by the motion vector detection unit 108. If the predictiondirection is bidirectional, an average of prediction signals in the L0direction and the L1 direction is generated as a prediction signal(S103).

The subtraction unit 102 calculates a difference between the picturesignal supplied by the prediction block picture deriving unit 101 theprediction signal supplied by the motion compensation unit 106 tocalculate a prediction error signal (S104). The prediction error encoder103 generates prediction error coding data by performing processing suchas quantization and orthogonal transformation on the prediction errorsignal supplied by the subtraction unit 102 (S105).

The bitstream generator 104 generates a bitstream by entropy-encodingthe prediction error coding data supplied by the prediction errorencoder 103 and the merge flag, merge candidate number, referencepicture index, vector difference, and vector predictor index supplied bythe motion information generator 109 together with the predictiondirection according to the syntax (S106).

The addition unit 107 generates a decoded picture signal by adding theprediction error signal supplied by the prediction error decoder 105 andthe prediction signal supplied by the motion compensation unit 106(S107). The frame memory 110 stores the decoded picture signal suppliedby the addition unit 107 (S108). The motion information memory 111stores one picture of the motion vector supplied by the motion vectordetection unit 108 in the minimum prediction block size unit (S109).

Subsequently, the operation of the motion information generator 109 willbe described using the flow chart in FIG. 21. The vector differencecalculation unit 120 decides a vector predictor index from a candidateblock group supplied from the terminal 12, a motion vector and areference picture index supplied from the terminal 13, a referencepicture supplied from the terminal 14, and a picture signal suppliedfrom the terminal 15 to calculate a vector difference and a ratedistortion evaluation value (S110).

The combined motion information decision unit 121 decides a mergecandidate number from the candidate block group supplied from theterminal 12, the reference picture supplied from the terminal 14, andthe picture signal supplied from the terminal 15 to calculate a ratedistortion evaluation value (S111).

The prediction coding mode decision unit 122 compares the ratedistortion evaluation value supplied by the vector differencecalculation unit 120 and the rate distortion evaluation value suppliedby the combined motion information decision unit 121. If the former issmaller than the latter, the merge flag is set to “0” and otherwise, themerge flag is set to “1” (S112).

Subsequently, the operation of the vector difference calculation unit120 will be described using the flow chart in FIG. 22. The vectorpredictor candidate list construction unit 130 constructs a vectorpredictor candidate list from candidate blocks obtained by deletingcandidate blocks outside the region, candidate blocks whose mode is theintra mode, and candidate blocks having duplicate motion vectors fromthe candidate block group supplied from the terminal 12. If theprediction direction is bidirectional, a vector predictor candidate listis constructed for the L0 direction and the L1 direction (S120).

The vector predictor decision unit 131 selects the optimum vectorpredictor to the motion vector supplied from the terminal 13 from thevector predictor candidate list supplied by the vector predictorcandidate list construction unit 130. If the prediction direction isbidirectional, the optimum vector predictor is selected for the L0direction and the L1 direction (S121). The subtraction unit 132calculates a vector difference by subtracting the vector predictorsupplied by the vector predictor decision unit 131 from the motionvector supplied from the terminal 13. If the prediction direction isbidirectional, a vector difference is calculated and supplied for the L0direction and the L1 direction (S122).

(Operation of the Combined Motion Information Decision Unit 121)

Subsequently, the operation of the combined motion information decisionunit 121 will be described in detail using the flow chart in FIG. 23.The combined motion information candidate generator 140 constructs acombined motion information candidate list from a candidate block groupsupplied from the terminal 12 (S130). The combined motion informationselection unit 141 decides the optimum combined motion information tothe motion vector reference picture index, and prediction directionsupplied from the terminal 13 from the combined motion informationcandidate generator 140 (S131).

(Operation of the Combined Motion Information Candidate Generator 140)

Subsequently, the operation of the combined motion information candidategenerator 140 will be described in detail using the flow chart in FIG.24. The unidirectional combined motion information candidate listconstruction unit 150 constructs a spatial combined motion informationcandidate list from candidate blocks obtained by deleting candidateblocks outside the region and candidate blocks whose mode in the intramode from a spatial candidate block group supplied from the terminal 12(S140). A detailed operation of constructing a spatial combined motioninformation candidate list will be described later.

The unidirectional combined motion information candidate listconstruction unit 150 constructs a temporal combined motion informationcandidate list from candidate blocks obtained by deleting candidateblocks outside the region and candidate blocks whose mode in the intramode from a temporal candidate block group supplied from the terminal 12(S141). A detailed operation of constructing a temporal combined motioninformation candidate list will be described later.

The unidirectional combined motion information candidate listconstruction unit 150 combines the spatial combined motion informationcandidate list and the temporal combined motion information candidatelist in the order of the merge candidate number to construct a firstcombined motion information candidate list (S142).

If a plurality of combined motion information candidates havingduplicate motion information is present in the first combined motioninformation candidate list supplied by the unidirectional combinedmotion information candidate list construction unit 150, the firstcombined motion information candidate list deletion unit 151 constructsa second combined motion information candidate list by retaining onecombined motion information candidate while deleting other combinedmotion information candidates (S143).

The bidirectional combined motion information candidate listconstruction unit 152 constructs a bidirectional combined motioninformation candidate list from the second combined motion informationcandidate list supplied by the first combined motion informationcandidate list deletion unit 151 (S144). A detailed operation ofconstructing a bidirectional combined motion information candidate listwill be described later.

The bidirectional combined motion information candidate listconstruction unit 152 constructs a third combined motion informationcandidate list by combining the second combined motion informationcandidate list and the bidirectional combined motion informationcandidate list in the order of merge candidate number (S145).

If a plurality of combined motion information candidates havingduplicate motion information is present in the third combined motioninformation candidate list supplied by the bidirectional combined motioninformation candidate list construction unit 152, the second combinedmotion information candidate list deletion unit 153 constructs acombined motion information candidate list by retaining one combinedmotion information candidate while deleting other combined motioninformation candidates (S146).

Subsequently, a detailed operation of constructing a spatial combinedmotion information candidate list will be described using the flow chartin FIG. 25. In the first embodiment, it is assumed that the spatialcombined motion information candidate list contains motion informationof smaller than or equal to four candidate blocks.

The following processing is repeatedly performed for the block A, blockB, block C, and block E as the four candidate blocks contained in thespatial candidate block group (S150 to S153). Whether each candidateblock is valid is inspected (S151). If a candidate block is not outsidethe region and whose mode is not the intra mode, the candidate block isvalid. If a candidate block is valid (YES in S151), motion informationof the candidate block is added to the spatial combined motioninformation candidate list (S152). If a candidate block is not valid (NOin S151), step S152 is skipped.

In the first embodiment, it is assumed that motion information ofsmaller than or equal to four candidate blocks is contained in thespatial combined motion information candidate list, but it is onlynecessary that the number of candidate blocks in the spatial combinedmotion information candidate list should fluctuate depending on validityof the candidate block and the present embodiment is not limited to theabove example.

Subsequently, a detailed operation of constructing a temporal combinedmotion information candidate list will be described using the flow chartin FIG. 26. In the first embodiment, it is assumed that the temporalcombined motion information candidate list contains motion informationof smaller than or equal to one candidate block.

The following processing is repeatedly performed for temporal blocks astwo candidate blocks contained in the temporal candidate block group(S160 to S166). Whether each candidate block is valid is inspected(S161). If a candidate block is not outside the region and whose mode isnot the intra mode, the candidate block is valid. If a candidate blockis valid (YES in S161), a temporal combined motion information candidateis generated and the temporal combined motion information candidate isadded to the temporal combined motion information candidate list (stepS162 to step S165) before the processing being terminated. If acandidate block is not valid (NO in S161), the next candidate block isinspected (S166).

If a candidate block is valid, the prediction direction of a temporalcombined motion information candidate is decided (S162). In the firstembodiment, the prediction direction of a temporal combined motioninformation candidate is assumed to be bidirectional. Next, thereference picture in the L0 direction and the L1 direction of thetemporal combined motion information candidate is decided (S163). In thefirst embodiment, the reference picture closest to the processing targetpicture of reference pictures in the L0 direction is defined as thereference picture in the L0 direction and the reference picture closestto the processing target picture of reference pictures in the L1direction is defined as the reference picture in the L1 direction. Whilethe reference picture closest to the processing target picture ofreference pictures in the L0 direction is defined as the referencepicture in the L0 direction and the reference picture closest to theprocessing target picture of reference pictures in the L1 direction isdefined as the reference picture in the L1 direction here, it is onlynecessary to be able to decide the reference picture in the L0 directionand the reference picture in the L1 direction and the present embodimentis not limited to the above example. For example, reference pictures inthe L0 direction or the L1 direction in a bitstream may be encoded,reference picture indexes in the L0 direction or the L1 direction may beset to 0, or most frequently used reference pictures of referencepictures in the L0 direction and reference pictures in the L1 directionused by neighboring blocks of the processing target block may be set asthe reference picture in the L0 direction and the L1 directionrespectively.

Next, a motion vector of the temporal combined motion informationcandidate is calculated (S164). For the temporal combined motioninformation candidate in the present embodiment, bidirectional motioninformation is calculated in reference to a reference picture ColRefPicand a motion vector mvCol in the prediction direction valid in motioninformation of the candidate block. If the prediction direction of thecandidate block is unidirectional (the L0 direction of the L1direction), a reference picture and a motion vector in the predictiondirection are selected as a reference. If the prediction direction ofthe candidate block is bidirectional, a reference picture and a motionvector in one of the L0 direction and the L1 direction are selected as areference. Various selections such as selecting a reference picture anda motion vector present in the same time direction as ColPic as areference, selecting a reference image in the L0 direction or the L1direction of the candidate block having a shorter inter-picture distanceto ColPic as a reference, and selecting a motion vector in the L0direction or the L1 direction of the candidate block crossing theprocessing target image as a reference can be considered. After thereference picture and the motion vector to be a reference for generatingbidirectional motion information are selected, a motion vector of thetemporal combined motion information candidate is calculated.

The temporal combined motion information candidate is generated asdescribed above here, but it is only necessary to be able to decidebidirectional motion information by using motion information of anotherencoded picture and the present embodiment is not limited to the aboveexample. For example, as is the case with the direct motioncompensation, a motion vector scaled in accordance with the distancebetween the reference picture in each direction and the processingtarget picture may be used as a bidirectional motion vector. If acandidate block is not valid (NO in S163), the next candidate block isinspected (S165).

It is assumed here that the temporal combined motion informationcandidate list contains motion information of smaller than or equal toone candidate block, but it is only necessary that the number ofcandidate blocks in the temporal combined motion information candidatelist should fluctuate depending on validity of the candidate block andthe present embodiment is not limited to the above example. The decisionmethods of the prediction direction, the reference picture, and themotion vector are similarly not limited to the above examples.

(Construction of a Bidirectional Combined Motion Information CandidateList)

Subsequently, a detailed operation of constructing a bidirectionalcombined motion information candidate list will be described using theflow chart in FIG. 27. It is assumed that the bidirectional combinedmotion information candidate list is empty. The reference directiondecision unit 160 decides the reference direction of a bidirectionalcombined motion information candidate from a second combined motioninformation candidate list (S170). The reference direction for thebidirectional combined motion information candidate (BD0) whosereference direction is L0 is the L0 direction and the referencedirection for the bidirectional combined motion information candidate(BD1) whose reference direction is L1 is the L1 direction.

The reference direction motion information decision unit 161 decides amotion vector and a reference picture index in the reference directionof the bidirectional combined motion information candidate from thereference direction and the second combined motion information candidatelist supplied by the reference direction decision unit 160 (S171). Adetailed operation of the reference direction motion informationdecision unit 161 will be described later.

The reverse direction motion information decision unit 162 decides amotion vector and a reference picture index in the reverse direction ofthe bidirectional combined motion information candidate from thereference direction, the motion vector and the reference picture indexin the reference direction, and the second combined motion informationcandidate list supplied by the reference direction motion informationdecision unit 161 (S172). A detailed operation of the reverse directionmotion information decision unit 162 will be described later.

The bidirectional motion information decision unit 163 decides theprediction direction of the bidirectional combined motion informationcandidate from the motion vector and the reference picture index in thereference direction and the motion vector and the reference pictureindex in the reverse direction supplied by the reverse direction motioninformation decision unit 162 (S173). A detailed operation of decidingthe prediction direction of a bidirectional combined motion informationcandidate list will be described later.

The bidirectional motion information decision unit 163 inspects thevalidity of the prediction direction of the bidirectional combinedmotion information candidate is valid (S174). If the predictiondirection of the bidirectional combined motion information candidate isvalid (YES in S174), the bidirectional motion information decision unit163 adds the bidirectional combined motion information candidate to thebidirectional combined motion information candidate list (S175). If theprediction direction of the bidirectional combined motion informationcandidate is invalid (NO in S174), step S175 is skipped.

Subsequently, a detailed operation of the reference direction motioninformation decision unit 161 will be described using the flow chart inFIG. 28. It is assumed that the LX direction (X is 0 or 1) is selectedas the reference direction of the bidirectional combined motioninformation candidate. The validity of LX as the reference direction isset to “0” (S190). The following processing is repeated as many times asthe number (NCands) of combined motion information candidates containedin the second combined motion information candidate list (S191 to S194).The validity of the LX direction of a combined motion informationcandidate is inspected (S192). If the LX direction of the combinedmotion information candidate is valid (YES in S192), the validity of LXas the reference direction is set to “1” and a motion vector and areference index in the reference direction are set as a motion vectorand a reference index in the LX direction of the combined motioninformation candidate before the processing being terminated (S193). Ifthe LX direction of the combined motion information candidate is invalid(NO in S192), the next candidate is inspected (S194).

It is assumed here that inspection is carried out as many times as thenumber (NCands) of combined motion information candidates contained inthe second combined motion information candidate list, but it is onlynecessary to be able to decide motion information in the referencedirection of the bidirectional combined motion information candidate andthe present embodiment is not limited to the above example. When, forexample, bidirectional combined motion information candidates aregenerated only from combined motion information candidates with a highselection rate, throughput can be reduced by fixing the number of timesof inspection to 2 or 3 and also code amount of merge indexes can bereduced by lowering the possibility of generating redundantbidirectional combined motion information candidates.

Subsequently, a detailed operation of the reverse direction motioninformation decision unit 162 will be described using the flow chart inFIG. 29. The reverse direction of the reference direction is set as thereverse direction of the bidirectional combined motion informationcandidate. It is assumed that the LY direction (Y is 0 or 1) isselected. The validity of LY as the reverse direction is set to “0”(S200). The following processing is repeated as many times as the number(NCands) of combined motion information candidates contained in thesecond combined motion information candidate list (S201 to S205).

That the combined motion information candidate is not a candidateselected for the reference direction is checked (S202). If the combinedmotion information candidate is different from a candidate selected forthe reference direction (YES in S202), the validity of the LY directionof the combined motion information candidate is inspected (S203). If theLY direction of the combined motion information candidate is valid (YESin S203), the validity of LY as the reverse direction is set to “1” anda motion vector and a reference index in the reverse direction are setas a motion vector and a reference index in the LY direction of thecombined motion information candidate before the processing beingterminated (S204). If the combined motion information candidate is acandidate selected for the reference direction (NO in S202) or the LYdirection of the combined motion information candidate is invalid (NO inS203), the next candidate is inspected (S205).

It is assumed here that inspection is carried out as many times as thenumber (NCands) of combined motion information candidates contained inthe second combined motion information candidate list, but it is onlynecessary to be able to decide motion information in the reversedirection of the bidirectional combined motion information candidate andthe present embodiment is not limited to the above example. When, forexample, bidirectional combined motion information candidates aregenerated only from combined motion information candidates with a highselection rate, throughput can be reduced by fixing the number of timesof inspection to 2 or 3 and also code amount of merge indexes can bereduced by lowering the possibility of generating redundantbidirectional combined motion information candidates. In addition, byselecting the block where the inspection is started as the next combinedmotion information candidate of the combined motion informationcandidate selected in the reference direction, the possibility that BD0and BD1 are the same is eliminated and so step S202 can be cut.

Subsequently, a detailed operation of deciding the prediction directionof a bidirectional combined motion information candidate will bedescribed using the table in FIG. 30. If both of the LX direction andthe LY direction are valid, the prediction direction is bidirectional(BI), if only the LX direction is valid, the prediction direction isunidirectional (LX direction), if only the LY direction is valid, theprediction direction is unidirectional (LY direction), and if both ofthe LX direction and the LY direction are invalid, the predictiondirection is invalid. That is, when both of the LX direction and the LYdirection are valid, a new bidirectional combined motion informationcandidate is generated after a combined motion information candidatehaving motion information in the LX direction and a combined motioninformation candidate having motion information in the LY direction,which is different from the combined motion information candidate havingmotion information in the LX direction, being combined. When only the LXdirection is valid, if the prediction direction of a combined motioninformation candidate having a valid LX prediction is a bidirectionalprediction, the prediction direction of the combined motion informationcandidate is converted into a unidirectional prediction. Similarly, whenonly the LY direction is valid, if the prediction direction of acombined motion information candidate having a valid LY prediction is abidirectional prediction, the prediction direction of the combinedmotion information candidate is converted into a unidirectionalprediction.

It is assumed here that the decision of the prediction direction of abidirectional combined motion information candidate follows FIG. 30, butit is only necessary to be able to decide the prediction direction andthe present embodiment is not limited to the above example. FIGS. 31A to31C show extension examples of the decision of the prediction directionof bidirectional combined motion information candidates. For example, asshown in FIG. 31A, the prediction direction may be invalidated if atleast one of the LX direction and the LY direction is invalid or, asshown in FIGS. 31B and 31C, the prediction direction may be forced to bebidirectional.

When the precision of a motion vector is relatively high, the predictionefficiency of a bidirectional prediction is generally higher than thatof a unidirectional prediction. Thus, if not both of the LX directionand the LY direction are valid in FIG. 31A, the code amount of mergeindexes can be reduced by invalidating the prediction direction of abidirectional combined motion information candidate to reduce the numberof combined motion information candidates. If, for example, there is abidirectional prediction candidate among unidirectional combined motioninformation candidates, adaptation processing to invalidate theprediction direction of the bidirectional combined motion informationcandidate may be adopted.

In FIG. 31B, a motion vector whose prediction direction is invalid isset to (0, 0) and a reference index is set to “0”. In this manner, abidirectional combined motion information candidate can be forced to bebidirectional by setting a reference picture of the shortest distance asa prediction signal. This is because “0” of the reference indexgenerally is the reference picture closest to the processing targetpicture and the reliability of the prediction signal of the shortestdistance is the highest.

(Configuration of the Moving Picture Decoding Device 200)

Next, a moving picture decoding device according to the first embodimentwill be described. FIG. 32 shows the moving picture decoding device 200according to the first embodiment. The moving picture decoding device200 is a device that decodes a bitstream encoded by the moving pictureencoding device 100 to generate reproduced pictures.

The moving picture decoding device 200 is realized by hardware such asan information processing apparatus including a CPU (Central ProcessingUnit), frame memory, and hard disk. The moving picture decoding device200 realizes functional elements described below with the above elementsoperating. The position information of the prediction block to bedecoded and the prediction block size are assumed to be shared insidethe moving picture decoding device 200 and are not illustrated. Themaximum number of combined motion information candidates contained inthe candidate number management table and the combined motioninformation candidate list is assumed to be shared in the moving picturedecoding device 200 and is not illustrated.

The moving picture decoding device 200 according to the first embodimentincludes a bitstream analysis unit 201, a prediction error decoder 202,an addition unit 203, a motion information reproducing unit 204, amotion compensation unit 205, a frame memory 206, and a motioninformation memory 207.

(Function of the Moving Picture Decoding Device 200)

The function of each unit will be described below. The bitstreamanalysis unit 201 decodes a bitstream supplied from a terminal 30 intoprediction error coding data, a merge flag, a merge candidate number,the prediction direction of a motion compensation prediction, areference picture index, a vector difference, and a vector predictorindex according to syntax. Then, the bitstream analysis unit suppliesthe prediction error coding data to the prediction error decoder 202 andthe merge flag, the merge candidate number, the prediction direction ofa motion compensation prediction, the reference picture index, thevector difference, and the vector predictor index to the motioninformation reproducing unit 204. Incidentally, the merge candidatenumber is obtained by converting the merge index.

The prediction error decoder 202 generates a prediction error signal byperforming processing such as inverse quantization and inverseorthogonal transformation on prediction error coding data supplied bythe bitstream analysis unit 201 and supplies the prediction error signalto the addition unit 203.

The addition unit 203 generates a decoded picture signal by adding theprediction error signal supplied by the prediction error decoder 202 anda prediction signal supplied by the motion compensation unit 205 andsupplies the decoded picture signal to the frame memory 206 and aterminal 31.

The motion information reproducing unit 204 reproduces motioninformation from the merge flag, merge candidate number, predictiondirection of a motion compensation prediction, reference picture index,vector difference, and vector predictor index supplied by the bitstreamanalysis unit 201 and supplies the motion information to the motioncompensation unit 205. A detailed configuration of the motioninformation reproducing unit 204 will be described later.

The motion compensation unit 205 generates a prediction signal by makingmotion compensation for a reference picture indicated by the referencepicture index in the frame memory 206 based on motion informationsupplied by the motion information reproducing unit 204. If theprediction direction is bidirectional, an average of prediction signalsin the L0 direction and the L1 direction is generated as a predictionsignal and the prediction signal is supplied to the addition unit 203.

The frame memory 206 and the motion information memory 207 have the samefunctions as the frame memory 110 and the motion information memory 111of the moving picture encoding device 100.

(Detailed Configuration of the Motion Information Reproducing Unit 204)

Subsequently, a detailed configuration of the motion informationreproducing unit 204 featuring the first embodiment will be describedusing FIG. 33. FIG. 33 shows the configuration of the motion informationreproducing unit 204. The motion information reproducing unit 204includes an encoding mode determination unit 210, a motion vectorreproducing unit 211, and a combined motion information reproducing unit212. A terminal 32 is connected to the encoding mode determination unit210, a terminal 33 is connected to the motion information memory 207,and a terminal 34 is connected to the motion compensation unit 205.

The function of each unit will be described below. If the merge flagsupplied by the bitstream analysis unit 201 is “0”, the encoding modedetermination unit 210 supplies the prediction direction of a motioncompensation prediction, a reference picture index, a vector difference,and a vector predictor index supplied by the bitstream analysis unit 201to the motion vector reproducing unit 211. If the merge flag is “1”, theencoding mode determination unit 210 supplies the merge candidate numbersupplied by the bitstream analysis unit 201 to the combined motioninformation reproducing unit 212.

The motion vector reproducing unit 211 reproduces motion informationfrom the prediction direction of a motion compensation prediction,reference picture index, vector difference, and vector predictor indexsupplied by the encoding mode determination unit 210 and a candidateblock group supplied from the terminal 33 and supplies the motioninformation to the terminal 34. A detailed configuration of the motionvector reproducing unit 211 will be described later.

The combined motion information reproducing unit 212 reproduces motioninformation from the merge candidate number supplied by the encodingmode determination unit 210 and the candidate block group supplied fromthe terminal 33 and supplies the motion information to the terminal 34.A detailed configuration of the combined motion information reproducingunit 212 will be described later.

Subsequently, a detailed configuration of the motion vector reproducingunit 211 will be described using FIG. 34. FIG. 34 shows theconfiguration of the motion vector reproducing unit 211. The motionvector reproducing unit 211 includes a vector predictor candidate listconstruction unit 220, a vector predictor decision unit 221, and anaddition unit 222. A terminal 35 is connected to the encoding modedetermination unit 210.

The function of each unit will be described below. The vector predictorcandidate list construction unit 220 has the same function as the vectorpredictor candidate list construction unit 130 of the moving pictureencoding device 100. The vector predictor decision unit 221 decides avector predictor from a vector predictor candidate list supplied by thevector predictor candidate list construction unit 220 and a vectorpredictor index supplied from the terminal 35 and supplies the vectorpredictor to the addition unit 222.

The addition unit 222 calculates a motion vector by adding a vectordifference supplied from the terminal 35 and the vector predictorsupplied by the vector predictor decision unit 221 and supplies themotion vector to the terminal 34.

Subsequently, a detailed configuration of the combined motioninformation reproducing unit 212 will be described using FIG. 35. FIG.35 shows the configuration of the combined motion informationreproducing unit 212. The combined motion information reproducing unit212 includes a combined motion information candidate generator 230 and acombined motion information selection unit 231.

The function of each unit will be described below. The combined motioninformation candidate generator 230 has the same function as thecombined motion information candidate generator 140 shown in FIG. 15.The combined motion information selection unit 231 selects motioninformation from a combined motion information candidate list based onthe combined motion information candidate list supplied by the combinedmotion information candidate generator 230 and a merge candidate numbersupplied from the terminal 35 and supplies the motion information to theterminal 34.

(Operation of the Moving Picture Decoding Device 200)

Subsequently, the operation of decoding by the moving picture decodingdevice 200 according to the first embodiment will be described using theflow chart in FIG. 36. The bitstream analysis unit 201 decodes abitstream supplied from the terminal 30 into prediction error codingdata, a merge flag, a merge candidate number, the prediction directionof a motion compensation prediction, a reference picture index, a vectordifference, and a vector predictor index according to syntax (S210).

The motion information reproducing unit 204 reproduces motioninformation from the merge flag, merge candidate number, predictiondirection of a motion compensation prediction, reference picture index,vector difference, and vector predictor index supplied by the bitstreamanalysis unit 201 (S211).

The motion compensation unit 205 generates a prediction signal by makingmotion compensation for a reference picture indicated by the referencepicture index in the frame memory 206 based on motion informationsupplied by the motion information reproducing unit 204. If theprediction direction is bidirectional, an average of prediction signalsin the L0 direction and the L1 direction is generated as a predictionsignal (S212).

The prediction error decoder 202 generates a prediction error signal byperforming processing such as inverse quantization and inverseorthogonal transformation on prediction error coding data supplied bythe bitstream analysis unit 201 (S213). The addition unit 203 generatesa decoded picture signal by adding the prediction error signal suppliedby the prediction error decoder 202 and the prediction signal suppliedby the motion compensation unit 205 (S214).

The frame memory 206 stores the decoded picture signal supplied by theaddition unit 203 (S215). The motion information memory 207 stores onepicture of the motion vector supplied by the motion informationreproducing unit 204 in the minimum prediction block size unit (S216).

Subsequently, the operation of the motion information reproducing unit204 will be described using the flow chart in FIG. 37. The encoding modedetermination unit 210 determines whether the merge flag supplied by thebitstream analysis unit 201 is “0” or “1” (S220). If the merge flag is“1” (1 in S220), the combined motion information reproducing unit 212reproduces motion information from a merge candidate number supplied bythe encoding mode determination unit 210 and a candidate block groupsupplied from the terminal 33 (S221).

If the merge flag is “0” (0 in S220), the motion vector reproducing unit211 reproduces motion information from the prediction direction of amotion compensation prediction, a reference picture index, a vectordifference, and a vector predictor index supplied by the encoding modedetermination unit 210 and the candidate block group supplied from theterminal 33 (S222).

Subsequently, the operation of the motion vector reproducing unit 211will be described using the flow chart in FIG. 38. The vector predictorcandidate list construction unit 220 constructs a vector predictorcandidate list by the same function as that of the vector predictorcandidate list construction unit 130 of the moving picture encodingdevice 100 (S300).

The vector predictor decision unit 221 decides a vector predictor byselecting the vector predictor indicated by a vector predictor indexsupplied from the terminal 35 from the vector predictor candidate listsupplied by the vector predictor candidate list construction unit 220(S301). The addition unit 222 calculates a motion vector by adding avector difference supplied from the terminal 35 and the vector predictorsupplied by the vector predictor decision unit 221 (S302).

Subsequently, the operation of the combined motion informationreproducing unit 212 will be described using the flow chart in FIG. 39.The combined motion information candidate generator 230 constructs acombined motion information candidate list by the same function as thatof the combined motion information candidate generator 140 of the movingpicture encoding device 100 (S310). The combined motion informationselection unit 231 decides combined motion information by selecting thecombined motion information candidate indicated by a merge candidatenumber supplied from the terminal 35 from the combined motioninformation candidate list supplied by the combined motion informationcandidate generator 230 (S311).

(Modifications of the First Embodiment)

The first embodiment can be modified as described below.

(First Modification: Order of the Merge Candidate Number)

In the first embodiment described above, FIG. 18 is cited as an exampleof the candidate number management table, it is only necessary that themaximum number of combined motion information candidates be larger thanor equal to 1 and a decreasing merge candidate number be assigned to acombined motion information candidate with an increasing selection rateand the candidate number management table is not limited to FIG. 18. Themaximum number of combined motion information candidates contained inthe combined motion information candidate list is assumed to be 7 (themaximum number of merge indexes is 6), but the maximum number thereofonly needs to be larger than or equal to 2. If, for example, theselection rate of a bidirectional combined motion information candidateis higher than the selection rate of a combined motion informationcandidate of the block C or the block E, the merge candidate number maybe assigned as shown in FIG. 40A or 40B.

In addition, as shown in FIG. 41, the bidirectional combined motioninformation candidates can be increased. Each bidirectional combinedmotion information candidate (BD0 to BD3) will be described. It isassumed that the bidirectional combined motion information candidate(BD0) and the bidirectional combined motion information candidate (BD1)are assumed to be the same as in the first embodiment. The bidirectionalcombined motion information candidate (BD2) and the bidirectionalcombined motion information candidate (BD3) are different from thebidirectional combined motion information candidate (BD0) and thebidirectional combined motion information candidate (BD1) in thedecision method of a motion vector and a reference index in thereference direction of a bidirectional combined motion informationcandidate in the reference direction and a motion vector and a referenceindex in the reference direction of a bidirectional combined motioninformation candidate in the reverse direction.

FIG. 42 is a flow chart illustrating derivation of the bidirectionalcombined motion information candidate (BD2). FIG. 42 is obtained byreplacing step S193 in the flow chart of FIG. 28 with steps S195 toS197. Hereinafter, steps S195 to S197 will be described. Whether thevalidity of LX is “1” is checked (S195). If the validity of LX is not“1” (NO in S195), the validity of LX is set to “1” (S196) and the nextcandidate is inspected (S194). If the validity of LX is “1” (YES inS195), a motion vector and a reference index in the reference directionare set as a motion vector and a reference index in the LX direction ofthe combined motion information candidate (S197) before the processingbeing terminated.

FIG. 43 is a flow chart illustrating derivation of the bidirectionalcombined motion information candidate (BD3). FIG. 43 is obtained byreplacing step S204 in the flow chart of FIG. 29 with steps S206 toS208. Hereinafter, steps S206 to S208 will be described. Whether thevalidity of LY is “1” is checked (S206). If the validity of LY is not“1” (NO in S206), the validity of LY is set to “1” (S207) and the nextcandidate is inspected (S205). If the validity of LY is “1” (YES inS206), a motion vector and a reference index in the reference directionare set as a motion vector and a reference index in the LY direction ofthe combined motion information candidate (S208) before the processingbeing terminated.

That is, the bidirectional combined motion information candidate (BD2)is a bidirectional combined motion information candidate using a motionvector and a reference index in the reference direction of the combinedmotion information candidate that becomes valid in the referencedirection as the second candidate and a motion vector and a referenceindex in the reverse direction of the combined motion informationcandidate that is not the same candidate in the reference direction andbecomes valid in the reverse direction as the first candidate.

That is, the bidirectional combined motion information candidate (BD3)is a bidirectional combined motion information candidate using a motionvector and a reference index in the reference direction of the combinedmotion information candidate that becomes valid in the referencedirection as the first candidate and a motion vector and a referenceindex in the reverse direction of the combined motion informationcandidate that is not the same candidate in the reference direction andbecomes valid in the reverse direction as the second candidate.

By increasing the combination of bidirectional combined motioninformation candidates as shown above, the encoding efficiency of motioninformation can be improved by increasing the selection rate of combinedmotion information candidates.

(Second Modification: Identity Determination of Bidirectional CombinedMotion Information Candidates)

In the first embodiment described above, FIG. 29 is cited as anoperation example of the reverse direction motion information decisionunit 162, but only a bidirectional combined motion information candidateneeds to be generated and the present embodiment is not limited to theabove example. For example, as shown in FIG. 44, step S240 is added forthe purpose of increasing validity of a bidirectional combined motioninformation candidate, that is, preventing deletion by the secondcombined motion information candidate list deletion unit 153.

That a combined motion information candidate having the same motioninformation as that of a bidirectional combined motion informationcandidate using a motion vector and a reference index in the referencedirection and a motion vector and a reference index in the reversedirection of the combined motion information candidate to be inspectedis absent in a second combined motion information candidate list ischecked (S240). If the same combined motion information candidate isabsent (YES in S240), step S205 is performed. If the same combinedmotion information candidate is not absent (NO in S240), the nextcandidate is inspected (S206). In this case, the second combined motioninformation candidate list deletion unit 153 in FIG. 16 and step S146 inFIG. 24 can be omitted.

Accordingly, a bidirectional combined motion information candidate willnot deleted by the second combined motion information candidate listdeletion unit 153 and the encoding efficiency of motion information canbe improved by increasing the selection rate of combined motioninformation candidates.

(Third Modification: Identity Determination in the Reference Directionof Bidirectional Combined Motion Information Candidates)

In the first embodiment described above, FIG. 29 is cited as anoperation example of the reverse direction motion information decisionunit 162, but as shown in FIG. 45, step S250 may be added.

That a motion vector and a reference index in the reverse direction of acombined motion information candidate selected in the referencedirection and a motion vector and a reference index in the reversedirection of the combined motion information candidate to be inspectedare not the same (S250). If the motion vectors and reference indexes arenot the same (YES in S250), step S205 is performed. If the motionvectors and reference indexes are the same (NO in S250), the nextcandidate is inspected (S206).

Accordingly, a bidirectional combined motion information candidate willnot be the same as a combined motion information candidate selected inthe reference direction and the encoding efficiency of motioninformation can be improved by increasing validity of the bidirectionalcombined motion information candidate and increasing the selection rateof the combined motion information candidate.

(Fourth Modification: Unification of the Deletion Process)

In the first embodiment described above, FIG. 16 is cited as an exampleof the configuration of the combined motion information candidategenerator 140, but as a simpler configuration, the deletion unit can beunified by, as shown in FIG. 46, retaining only the second combinedmotion information candidate list deletion unit 153 while eliminatingthe first combined motion information candidate list deletion unit 151.

In this case, however, redundant combined motion information candidatesare supplied to the bidirectional combined motion information candidatelist construction unit 152 and thus, if the first two unidirectionalcombined motion information candidates are the same, the bidirectionalcombined motion information candidate (BD0) whose reference direction isL0 and the bidirectional combined motion information candidate (BD1)whose reference direction is L1 become the same motion information.Therefore, as shown in FIG. 47B, the probability of generating the samebidirectional combined motion information candidate can be lowered bychanging the inspection order in FIGS. 28 and 29 depending on whetherthe reference direction is L0 or L1.

Fifth Embodiment: Using the Same Direction

In the first embodiment described above, regarding the reverse directionof the reverse direction motion information decision unit 162, anexample in which the reverse direction becomes the L1 direction if thereference direction is the L0 direction and the reverse directionbecomes the L0 direction if the reference direction is the L1 directionis cited. In this respect, the L0 direction may be set as the reversedirection if the reference direction is the L0 direction and the L1direction may be set as the reverse direction if the reference directionis the L1 direction. When, as shown in FIG. 48, only motion informationof the same prediction direction is present in combined motioninformation candidates contained in the second combined motioninformation candidate list, the encoding efficiency of motioninformation can be improved by increasing the probability of generatinga bidirectional combined motion information candidate and increasing theselection rate of a combined motion information candidate.

(Sixth Modification: Preset Combination)

In the first embodiment described above, a bidirectional combined motioninformation candidate is generated by searching for combined motioninformation candidate blocks that are valid in the reference directionand the reverse direction and using motion information in the referencedirection and the reverse direction. While the validity of abidirectional combined motion information candidate can be improved byperforming a search in the reference direction and the reversedirection, the throughput increases.

Thus, by defining a bidirectional combined motion information candidate,as shown in FIGS. 49A and 49B, as a preset combination of highlyreliable combined motion information candidate blocks, the encodingefficiency can be improved by omitting search processing and improvingthe selection rate of a bidirectional combined motion informationcandidate.

FIG. 49A is an example in which the prediction direction of thebidirectional combined motion information candidate (BD0) whosereference direction is L0 is defined as a bidirectional prediction bycombining motion information in the L0 direction of the most reliablecandidate block A and motion information in the L1 direction of thesecond most reliable candidate block B, and the prediction direction ofthe bidirectional combined motion information candidate (BD1) whosereference direction is L1 is defined as a bidirectional prediction bycombining motion information in the L1 direction of the most reliablecandidate block A and motion information in the L0 direction of thesecond most reliable candidate block B.

FIG. 49B is an example of defining the prediction direction as aunidirectional prediction in which the bidirectional combined motioninformation candidate (BD0) whose reference direction is L0 is definedas motion information in the L0 direction of the most reliable candidateblock A and the bidirectional combined motion information candidate(BD1) whose reference direction is L1 is defined as motion informationin the L1 direction of the most reliable candidate block A. Othercombinations are also allowed if more reliable candidate blocks arecombined.

(Seventh Modification: BD0, BD1 Adaptation)

In the first embodiment described above, a smaller merge candidatenumber is assigned to the bidirectional combined motion informationcandidate (BD0) whose reference direction is L0, but the presentembodiment is not limited to such an example. For example, the encodingefficiency can also be improved by preferentially assigning a smallermerge candidate number to a bidirectional combined motion informationcandidate whose prediction direction is bidirectional to assign asmaller merge candidate number to a bidirectional combined motioninformation candidate of bidirectional prediction with high predictionefficiency. Further, when both of BD0 and BD1 are bidirectionalpredictions, a smaller merge candidate number can preferentially beassigned to a bidirectional combined motion information candidate whosemotion information in the reference direction is unidirectional. This isbecause if a unidirectional prediction is selected even if abidirectional prediction has higher prediction efficiency than aunidirectional prediction, the reliability of motion information thereofis high.

(Effect of the First Embodiment)

(Effect Example of Bidirectional Combined Motion Information of aBidirectional Prediction)

The effect of the first embodiment will be described using FIG. 50.Hereinafter, the motion vector in the L0 direction of a block N isrepresented as mvL0N, the motion vector in the L1 direction as mvL1N,the reference picture index in the L0 direction as refIdxL0N, thereference picture index in the L1 direction as refIdxL1N, the vectordifference in the L0 direction as dmvL0N, the vector difference in theL1 direction as dmvL1N, the difference of reference picture indexes inthe L0 direction as drefIdxL0N, and the difference of reference pictureindexes in the L1 direction as drefIdxL1N.

The motion information that minimizes the prediction error for theprocessing target block (Z) is assumed that the prediction direction isbidirectional (BI), mvL0Z=(2,8), mvL1Z=(4,2), refIdxL0Z=0, andrefIdxL1N=0.

In this case, unidirectional combined motion information candidates areassumed to be A, B, COL, C, and E in FIG. 50. Among these unidirectionalcombined motion information candidates, there is no motion informationthat minimizes the prediction error for the processing target block (Z).Thus, the unidirectional combined motion information candidate thatminimizes the rate distortion evaluation value will be selected fromthese unidirectional combined motion information candidates. Then, therate distortion evaluation value of the selected candidate and the ratedistortion evaluation value calculated by the vector differencecalculation unit 120 are compared and the merge mode is used as theencoding mode only if the former is smaller than the latter.

When the merge mode is selected as the encoding mode, it is because ofthe optimum balance between the encoding efficiency of motioninformation and a prediction error and the prediction error is not theoptimum error. On the other hand, when a non-merge mode is selected asthe encoding mode, the encoding efficiency of motion information is notthe optimum efficiency.

Here, bidirectional combined motion information candidates generatedaccording to the first embodiment include BD0 and BD1 in FIG. 50. Thebidirectional combined motion information candidate (BD0) whosereference direction is L0 is a bidirectional combined motion informationcandidate formed from motion information in the L0 direction of theblock A and motion information in the L1 direction of the block B. Thebidirectional combined motion information candidate (BD1) whosereference direction is L1 is a bidirectional combined motion informationcandidate formed from motion information in the L1 direction of theblock A and motion information in the L0 direction of the block B. Inthis case, it is clear that the bidirectional combined motioninformation candidate (BD0) whose reference direction is L0 has the samemotion information as the motion information that minimizes theprediction error for the processing target block (Z). That is, byselecting the bidirectional combined motion information candidate (BD0)whose reference direction is L0, it becomes possible to minimize theprediction error and optimize the encoding efficiency of motioninformation.

(Effect Example of Bidirectional Combined Motion Information of aUnidirectional Prediction)

The effect of a unidirectional prediction according to the firstembodiment will be described using FIG. 51. The motion information thatminimizes the prediction error for the processing target block (Z) isassumed that the prediction direction is unidirectional (UNI),mvL0Z=(0,8), and refIdxL0Z=2.

It is assumed that the unidirectional combined motion informationcandidates B, C, COL are invalid (X) and the valid unidirectionalcombined motion information candidates A, E have motion information asshown in FIG. 51. Also in this case, among unidirectional combinedmotion information candidates, there is no motion information thatminimizes the prediction error for the processing target block (Z).

Here, bidirectional combined motion information candidates generatedaccording to the first embodiment also include BD0 and BD1 in FIG. 51.The bidirectional combined motion information candidate (BD0) whosereference direction is L0 is a bidirectional combined motion informationcandidate formed from motion information in the L0 direction of theblock A and whose prediction direction is unidirectional. Thebidirectional combined motion information candidate (BD1) whosereference direction is L1 is a bidirectional combined motion informationcandidate formed from motion information in the L0 direction of theblock E and motion information in the L1 direction of the block A. It isclear that the bidirectional combined motion information candidate (BD0)whose reference direction is L0 has the same motion information as themotion information that minimizes the prediction error for theprocessing target block (Z). That is, by selecting the bidirectionalcombined motion information candidate (BD0) whose reference direction isL0, it becomes possible to minimize the prediction error and optimizethe encoding efficiency of motion information.

(Effect Example of Bidirectional Combined Motion Information by aCombination of Unidirectional Predictions)

The effect of combining motion information whose prediction direction isunidirectional according to the first embodiment will be described usingFIG. 52. The motion information that minimizes the prediction error forthe processing target block (Z) is assumed that the prediction directionis bidirectional (BI), mvL0Z=(2,2), refIdxL0Z=0, mvL1Z=(−2,2), andrefIdxL1Z=0.

It is assumed that the unidirectional combined motion informationcandidates A, COL, C are invalid (X) and the valid unidirectionalcombined motion information candidates B, E have motion information asshown in FIG. 52. Also in this case, among unidirectional combinedmotion information candidates, there is no motion information thatminimizes the prediction error for the processing target block (Z).

Here, bidirectional combined motion information candidates generatedaccording to the first embodiment also include BD0 and BD1 in FIG. 52.The bidirectional combined motion information candidate (BD0) whosereference direction is L0 is a bidirectional combined motion informationcandidate formed from motion information in the L0 direction of theblock B and motion information in the L1 direction of the block E. It isclear that the bidirectional combined motion information candidate (BD0)whose reference direction is L0 has the same motion information as themotion information that minimizes the prediction error for theprocessing target block (Z). That is, by selecting the bidirectionalcombined motion information candidate (BD0) whose reference direction isL0, it becomes possible to minimize the prediction error and optimizethe encoding efficiency of motion information.

(Bidirectional Combined Motion Information Candidate)

By generating a bidirectional combined motion information candidateusing motion information in the L0 direction and the L1 direction ofunidirectional combined motion information candidates as describedabove, encoding can be performed using only the index without encodingmotion information even if the motion of the processing target block isshifted from the motion of the block in the same position of anotherencoded picture or neighboring blocks of the processing target block.Therefore, a moving picture encoding device and a moving picturedecoding device capable of optimizing the encoding efficiency andprediction efficiency can be realized.

(Unidirectional Combined Motion Information Candidate)

Also when a new unidirectional combined motion information candidate isgenerated using motion information in the L0 direction and the L1direction of unidirectional combined motion information candidates, thesame effect as when a new bidirectional combined motion informationcandidate is generated using motion information in the L0 direction andthe L1 direction of unidirectional combined motion informationcandidates is achieved.

(Bidirectional Combined Motion Information Using the Same Direction)

Also when a bidirectional combined motion information candidate isgenerated using motion information in the same prediction direction ofunidirectional combined motion information candidates, the same effectas when a bidirectional combined motion information candidate isgenerated using motion information in the L0 direction and the L1direction of unidirectional combined motion information candidates isachieved.

(Simplification of the Moving Picture Decoding Processing)

By generating a bidirectional combined motion information candidateusing motion information in each direction of unidirectional combinedmotion information candidates as described above, even if the motion ofthe processing target block is shifted from the motion of the block inthe same position of another encoded picture or neighboring blocks ofthe processing target block, the need for decoding the predictiondirection, reference index, and vector difference and additionprocessing of the vector predictor and vector difference can beeliminated so that processing of the moving picture decoding device canbe reduced.

(Deletion Process)

By setting up the first combined motion information candidate listdeletion unit 151, bidirectional combined motion information candidate(BD0) whose reference direction is L0 and the bidirectional combinedmotion information candidate (BD1) whose reference direction is L1 canbe prevented from having the same motion information in thebidirectional combined motion information candidate list constructionunit 152 and the encoding efficiency can be improved by increasingvalidity of bidirectional combined motion information candidates.

(Merge Candidate Number Assignment in Order of Selection Rate)

By assigning a decreasing merge candidate number to a combined motioninformation candidate with an increasing selection rate, it becomespossible to increase the selection rate of more probable motioninformation in each direction and to generate a high-precisionbidirectional combined motion information candidate using highly precisemotion information in each direction. In addition, the processing ofsearch can be simplified and a decrease of the encoding efficiency canbe inhibited even if the number of processing of search is limited.

(Memory Lead Time)

By generating bidirectional combined motion information candidate usingmotion information in each direction of unidirectional combined motioninformation candidates as described above, the number of combined motioninformation candidates can be increased without increasing the number ofunidirectional combined motion information candidates. Therefore, in amoving picture encoding device and a moving picture decoding deviceusing a general LSI in which the memory lead time increases with anincreasing number of unidirectional combined motion informationcandidates, an increase of the memory lead time due to an increase ofthe number of unidirectional combined motion information candidates canbe inhibited.

(Adaptation Switching)

By preferentially assigning a smaller merge candidate number to abidirectional combined motion information candidate whose predictiondirection is bidirectional, the selection rate of a bidirectionalcombined motion information candidate whose prediction efficiency ishigh and whose prediction direction is bidirectional can be increased,and by preferentially assigning a smaller merge candidate number to abidirectional combined motion information candidate whose motioninformation in the prediction direction is unidirectional, the encodingefficiency can be improved by increasing the selection rate of abidirectional combined motion information candidate using highlyreliable motion information.

Second Embodiment

(Syntax)

The configuration of a moving picture encoding device according to thesecond embodiment is the same as the configuration of the moving pictureencoding device according to the first embodiment excluding an upperfunction of the moving picture encoding device and the function of thebitstream generator 104. Hereinafter, differences of the upper functionof the moving picture encoding device in the second embodiment and thefunction of the bitstream generator 104 from those in the firstembodiment will be described.

The upper function of the moving picture encoding device in the secondembodiment has a function to change a candidate number management tablein bitstream units or for each slice as a portion of a bitstream. Thebitstream generator 104 transmits a candidate number management table byencoding the table, as shown in FIGS. 53A and 53B, in a bitstream. FIGS.53A and 53B shows examples of syntax that encodes a candidate numbermanagement table based on SPS (Sequence Parameter Set) for the controlin bitstream units and Slice_header for the control in slice unitsrespectively.

“modified_merge_index_flag” specifies whether to change the standardrelationship of the merge candidate number and combined motioninformation candidate, “max_no_of_merge_index_minus1” specifies thenumber of redefinitions, and “merge_mode [i]” specifies the order ofcandidate blocks contained in a combined motion information candidatelist. In addition, “bd_merge_base_direction” as information to specifythe reference direction of a bidirectional combined motion informationcandidate can be set up.

For example, it is assumed that the standard relationship between themerge candidate number and the combined motion information candidate isgiven by FIG. 18 and the candidate number management table to beredefined is given by FIG. 40A.

FIGS. 53A and 53B are examples of syntax and the syntax only needs to beable to specify the merge candidate number assigned to a bidirectionalcombined motion information candidate in a bitstream and specifying thereference direction of the bidirectional combined motion informationcandidate and is not limited to the above examples.

The configuration of a moving picture decoding device according to thesecond embodiment is the same as the configuration of the moving picturedecoding device 200 according to the first embodiment excluding thefunction of the bitstream analysis unit 201. Hereinafter, a differenceof the function of the bitstream analysis unit 201 of the moving picturedecoding device according to the second embodiment from that in thefirst embodiment will be described. The bitstream analysis unit 201decodes a candidate number management table according to the syntax inFIGS. 53A and 53B.

(Effect of the Second Embodiment)

By sharing the optimum relationship between the merge candidate numberand the combined motion information candidate in stream units or sliceunits by the moving picture encoding device and the moving picturedecoding device according to the second embodiment, the encodingefficiency of the merge index can be improved when characteristics ofmotion change in stream units or slice units.

Third Embodiment

(Replacement of Combined Motion Information Candidates)

The configuration of a moving picture encoding device according to thethird embodiment is the same as the configuration of the moving pictureencoding device 100 according to the first embodiment excluding thefunction of the combined motion information candidate generator 140.First, it is assumed that the candidate number management table in thethird embodiment is given by FIG. 54 and the maximum number of combinedmotion information candidates contained in a combined motion informationcandidate list is 5. The third embodiment is different in that themaximum number of combined motion information candidates contained in acombined motion information candidate list is 5 and no merge candidatenumber is assigned to a bidirectional combined motion informationcandidate. Hereinafter, a difference of the combined motion informationcandidate generator 140 in the third embodiment from that in the firstembodiment will be described using FIG. 55.

The combined motion information candidate generator 140 in FIG. 55 has aconfiguration in which a candidate number management table changing unit154 is added to the combined motion information candidate generator 140in FIG. 16. Hereinafter, the function of the candidate number managementtable changing unit 154 will be described. The candidate numbermanagement table changing unit 154 calculates the valid number ofbidirectional combined motion information candidates from a secondcombined motion information candidate list supplied by the combinedmotion information candidate list deletion unit 151. If the valid numberof bidirectional combined motion information candidates is larger thanor equal to 1, the candidate number management table is changed and thesecond combined motion information candidate list is supplied to thebidirectional combined motion information candidate list constructionunit 152. If the valid number of bidirectional combined motioninformation candidates is 0, the second combined motion informationcandidate list is supplied to the terminal 18 as a combined motioninformation candidate list.

Hereinafter, a difference of the operation of the combined motioninformation candidate generator 140 in the third embodiment from that inthe first embodiment will be described using FIG. 56. The flow chart inFIG. 56 is obtained by adding the following two steps to the flow chartin FIG. 24. The candidate number management table changing unit 154changes the candidate number management table (S260). Whether thecandidate number management table is changed is checked (S261). If thecandidate number management table is changed (YES in S261), step S144 isperformed. If the candidate number management table is not changed (NOin S261), step S144 is skipped.

Hereinafter, the operation of the candidate number management tablechanging unit 154 will be described using FIG. 57. First, the candidatenumber management table changing unit 154 counts the number of invalidcombined motion information candidates that are not contained in thesecond combined motion information candidate list to calculate theinvalid number of combined motion information candidates (S270). In thethird embodiment, the invalid number of combined motion informationcandidates is set as the number of invalid combined motion informationcandidates contained in the second combined motion information candidatelist, but it is only necessary to be able to calculate the number ofinvalid combined motion information candidates and the presentembodiment is not limited to the above example. For example, the numberof invalid combined motion information candidates may be determined bysubtracting the number of valid combined motion information candidatescontained in the second combined motion information candidate list from5, which is the total of the maximum number 4 of spatial combined motioninformation candidates and the maximum number 1 of temporal combinedmotion information candidates. When combined motion information with ahigh selection rate is invalid, the selection rate of a bidirectionalcombined motion information candidate is expected to decrease and thus,the number of invalid combined motion information candidates whose mergecandidate number is larger than or equal to 2 may be counted.

The candidate number management table changing unit 154 checks whetherthe invalid number of combined motion information candidates is largerthan or equal to 1 (S271). If the invalid number of combined motioninformation candidates is larger than or equal to 1 (YES in S271), thesubsequent processing is performed to change the candidate numbermanagement table. If the invalid number of combined motion informationcandidates is 0 (NO in S271), the processing is terminated.

The candidate number management table changing unit 154 counts thenumber of valid bidirectional combined motion information candidates tocalculate the valid number of bidirectional combined motion informationcandidates (S272). That is, when both of BD0 and BD1 are valid, thevalid number of bidirectional combined motion information candidates is2, when one of BD0 and BD1 is valid, the valid number of bidirectionalcombined motion information candidates is 1, and when both of BD0 andBD1 are invalid, the valid number of bidirectional combined motioninformation candidates is 0.

The candidate number management table changing unit 154 sets the smallerof the invalid number of combined motion information candidates and thevalid number of bidirectional combined motion information candidates asan addition number of bidirectional combined motion informationcandidates (S273). The candidate number management table changing unit154 assigns invalid merge candidate numbers to as many bidirectionalcombined motion information candidates as the addition number ofbidirectional combined motion information candidates (S274).

Hereinafter, change examples of the candidate number management table bythe candidate number management table changing unit 154 will bedescribed using FIGS. 58A to 58C. FIG. 58A shows an example in which theinvalid number of combined motion information candidates is 1 and thevalid number of bidirectional combined motion information candidates islarger than or equal to 1. BD0 is assigned to the first invalid mergecandidate number 1. If BD1 is valid, BD1 may be assigned. FIG. 58B showsan example in which the invalid number of combined motion informationcandidates is 2 and the valid number of bidirectional combined motioninformation candidates is 2. BD0 is assigned to the first invalid mergecandidate number 2 and BD1 is assigned to the second invalid mergecandidate number 4. FIG. 58C shows an example in which the invalidnumber of combined motion information candidates is 2 and the validnumber of bidirectional combined motion information candidates is 1 (BD1is valid). BD1 is assigned to the first invalid merge candidate number2.

The configuration of a moving picture decoding device according to thethird embodiment is the same as the configuration of the moving picturedecoding device 200 according to the first embodiment excluding thefunction of the combined motion information candidate generator 140. Thecombined motion information candidate generator 140 of the movingpicture decoding device according to the third embodiment is the same asthe combined motion information candidate generator 140 of a movingpicture encoding device according to the third embodiment.

(Modifications of the Third Embodiment)

The third embodiment can be modified as described below.

(First Modification: Unidirectional Combined Motion InformationCandidate Precedence)

In the third embodiment described above, FIG. 57 is cited as anoperation example of the candidate number management table changing unit154, but the changed candidate number management table is only requiredthat a decreasing merge candidate number should be assigned to acombined motion information candidate with an increasing selection rateand the present embodiment is not limited to the above table.

If, for example, the reliability of existing unidirectional combinedmotion information candidates is sufficiently high, as shown in FIG. 59,step S275 shown below may be added to the operation of the candidatenumber management table changing unit 154. The flow chart in FIG. 59 isobtained by adding step S275 to the flow chart in FIG. 57. The candidatenumber management table changing unit 154 skips the merge candidatenumbers of invalid combined motion information candidates (S274).

Hereinafter, change examples of the candidate number management table bythe candidate number management table changing unit 154 will bedescribed using FIGS. 60A and 60B. FIG. 60A shows an example in whichthe invalid number of combined motion information candidates is 1 andthe valid number of bidirectional combined motion information candidatesis larger than or equal to 1. After an invalid merge candidate number(merge candidate number 1) being skipped, BD0 is assigned to the firstinvalid merge candidate number 4. If BD1 is valid, BD1 may be assigned.FIG. 60B shows an example in which the invalid number of combined motioninformation candidates is 2 and the valid number of bidirectionalcombined motion information candidates is 2. After an invalid mergecandidate number (merge candidate number 2) being skipped, BD0 isassigned to the first invalid merge candidate number 3 and BD1 isassigned to the second invalid merge candidate number 4. In this manner,a larger merge candidate number is assigned to a bidirectional combinedmotion information candidate than a unidirectional combined motioninformation candidate.

(Second Modification: Predetermined Block Dependency)

The operation of the candidate number management table changing unit 154can further be modified. First, it is assumed in the presentmodification that a predetermined bidirectional combined motioninformation candidate is associated with a predetermined block and BD0is associated with the block C and BD1 is associated with the block D.Hereinafter, another modification of the operation of the candidatenumber management table changing unit 154 will be described using FIG.61. The following processing is repeated as many times as the number ofassociated blocks (S280 to S284). Check whether the i-th predeterminedblock is invalid (S281). If the i-th predetermined block is invalid (YESin S281), the subsequent processing is performed to change the candidatenumber management table. If the i-th predetermined block is not invalid(NO in S281), the next predetermined block is inspected.

In the second modification, predetermined combined motion informationcandidates are assumed to be two blocks of the block C of the mergecandidate number 3 and the block E of the merge candidate number 4.Thus, the candidate number management table changing unit 154 assignsthe bidirectional combined motion information candidate (BD0) to thefirst predetermined invalid merge candidate number and the bidirectionalcombined motion information candidate (BD1) to the second predeterminedinvalid merge candidate number (S282).

As described above, in the bidirectional combined motion informationcandidate list construction unit 152 according to the secondmodification, when a predetermined combined motion information candidateis invalid, a bidirectional combined motion information candidatebecomes valid. The block C and the block E are assumed to bepredetermined combined motion information candidates, but it is onlynecessary that a bidirectional combined motion information candidateshould be generated when a combined motion information candidate havinga larger merge candidate number and a low selection rate is invalid.

(Third Modification: Replacement of Combined Motion InformationCandidates of the Unidirectional Prediction)

The operation of the candidate number management table changing unit 154can further be modified. Hereinafter, a modification of the operation ofthe candidate number management table changing unit 154 will bedescribed using FIG. 62. If the invalid number of combined motioninformation candidates is 0 (NO in S271), the candidate numbermanagement table changing unit 154 counts combined motion informationcandidates contained in the second combined motion information candidatelist and whose prediction direction is unidirectional (the L0 directionor the L1 direction) to calculate the number of unidirectionalpredictions. Whether the number of unidirectional predictions is largerthan or equal to 1 (S291). If the valid number of unidirectionalcombined motion information candidates is larger than or equal to 1 (YESin S291), the subsequent processing is performed to change the candidatenumber management table. If the number of unidirectional predictions is0 (NO in S291), the processing is terminated. The candidate numbermanagement table changing unit 154 counts the number of bidirectionalcombined motion information candidates whose prediction direction isbidirectional to calculate the valid number of bidirectional combinedmotion information candidates (S292). The candidate number managementtable changing unit 154 assigns merge candidate numbers of combinedmotion information candidates whose prediction direction isunidirectional to as many bidirectional combined motion informationcandidates as the addition number of bidirectional combined motioninformation candidates (S294).

As a concrete example, if the prediction direction of the bidirectionalcombined motion information candidate (BD0) is bidirectional, thecandidate number management table changing unit 154 assigns the lastmerge candidate number whose prediction direction is unidirectional tothe bidirectional combined motion information candidate (BD0). If thedirection of motion compensation prediction of the bidirectionalcombined motion information candidate (BD1) is bidirectional, thecandidate number management table changing unit 154 assigns the secondlast merge candidate number whose prediction direction is unidirectionalto the bidirectional combined motion information candidate (BD1). In thethird modification of the third embodiment, the number of unidirectionalpredictions is set as the number of combined motion informationcandidates contained in the second combined motion information candidatelist and whose prediction direction is unidirectional, but it is onlynecessary to be able to calculate the number of unidirectionalpredictions and the present modification is not limited to the aboveexample. For example, combined motion information with a high selectionrate is considered to be highly reliable even if its predictiondirection is unidirectional and thus, the number of combined motioninformation candidates whose merge candidate number is larger than orequal to 3 and whose prediction direction is unidirectional. If theinvalid number of combined motion information candidates is 0, thenumber of combined motion information candidates whose predictiondirection is unidirectional is counted, it is only necessary to be ableto assign a merge candidate number to a bidirectional combined motioninformation candidate with the total number of the invalid number ofcombined motion information candidates and the number of unidirectionalpredictions set as an upper limit.

As described above, the bidirectional combined motion informationcandidate list construction unit 152 according to the third embodimentreplaces a combined motion information candidate whose predictiondirection is unidirectional with a bidirectional combined motioninformation candidate whose prediction direction is bidirectional.

(Effect of the Third Embodiment)

By using an invalid merge index as a merge candidate number of abidirectional combined motion information candidate as described above,an increase of the code amount of merge indexes due to an increase ofthe merge candidate numbers can be inhibited and the encoding efficiencycan be improved by increasing the selection rate of a combined motioninformation candidate.

When the reliability of motion information in the time direction orspace direction is high, as described above, the encoding efficiency ofmerge indexes can be improved by using the merge candidate number suchthat the merge candidate number of a bidirectional combined motioninformation candidate becomes larger than the merge candidate number ofa unidirectional combined motion information candidate.

By associating a combined motion information candidate having a largemerge candidate number with a bidirectional combined motion informationcandidate, as described above, while retaining combined motioninformation candidates of blocks having high reliability and a highselection rate, a combined motion information candidate having a lowselection rate and a bidirectional combined motion information candidatecan adaptively be switched. Therefore, an increase of the code amount ofmerge indexes due to an increase of the merge candidate numbers can beinhibited and the encoding efficiency can be improved by increasing theselection rate of a combined motion information candidate.

By replacing a combined motion information candidate whose predictiondirection is unidirectional with a bidirectional combined motioninformation candidate whose prediction direction is bidirectional, asdescribed above, the number of bidirectional combined motion informationcandidates having high prediction efficiency and whose predictiondirection is bidirectional can be increased and the encoding efficiencycan be improved by increasing the selection rate of a combined motioninformation candidate.

Fourth Embodiment

(Precedence of Motion Information of the Unidirectional Prediction)

The configuration of a moving picture encoding device according to thefourth embodiment is the same as the configuration of the moving pictureencoding device 100 according to the first embodiment excluding thefunction of the reference direction motion information decision unit161. Hereinafter, a difference of the reference direction motioninformation decision unit 161 in the fourth embodiment from that in thefirst embodiment will be described. The operation of the referencedirection motion information decision unit 161 in the fourth embodimentwill be described using FIG. 63.

The flow chart in FIG. 63 is obtained by adding steps S320 to S323 tothe flow chart in FIG. 28 and features step S321. First, the validity ofLX as the reference direction is set to “0” (S190). The followingprocessing is repeated as many times as the number (NCands) of combinedmotion information candidates contained in the second combined motioninformation candidate list (S320 to S323). The validity of the LXdirection of a combined motion information candidate and whether theprediction direction thereof is a unidirectional prediction are checked(S321). If the LX direction of the combined motion information candidateis valid and the prediction direction thereof is a unidirectionalprediction (YES in S321), the validity of LX as the reference directionis set to “1” and a motion vector and a reference index in the referencedirection are set as a motion vector and a reference index in the LXdirection of the combined motion information candidate before theprocessing being terminated (S322). If the LX direction of the combinedmotion information candidate is valid and the prediction directionthereof is not a unidirectional prediction (NO in S321), the nextcandidate is inspected (S323).

If the LX direction of a combined motion information candidates is validand a motion information candidate of the unidirectional prediction isnot present, the following processing is repeated as many times as thenumber (NCands) of combined motion information candidates contained inthe second combined motion information candidate list (S191 to S194).The validity of the LX direction of a combined motion informationcandidate is inspected (S192). If the LX direction of the combinedmotion information candidate is valid (YES in S192), the validity of LXas the reference direction is set to “1” and a motion vector and areference index in the reference direction are set as a motion vectorand a reference index in the LX direction of the combined motioninformation candidate before the processing being terminated (S193). Ifthe LX direction of the combined motion information candidate is invalid(NO in S192), the next candidate is inspected (S194). Thus, thereference direction motion information decision unit 161 in the fourthembodiment is different from that in the first embodiment in thatunidirectional motion information takes precedence in the decision ofmotion information in the reference direction.

The configuration of a moving picture decoding device according to thefourth embodiment is the same as the configuration of the moving picturedecoding device 200 according to the first embodiment excluding thefunction of the reference direction motion information decision unit161. The combined motion information candidate generator 140 of themoving picture decoding device according to the fourth embodiment is thesame as the combined motion information candidate generator 140 of amoving picture encoding device according to the fourth embodiment.

(Modifications of the Fourth Embodiment)

The fourth embodiment can be modified as described below.

(First Modification: Limited to Unidirectional)

In the fourth embodiment described above, FIG. 63 is cited as anoperation example of the reference direction motion information decisionunit 161, but it is only necessary that unidirectional motioninformation should take precedence in the decision of motion informationand the present embodiment is not limited to such an example. Forexample, motion information in the reference direction may be limited tounidirectional motion information by deleting steps S191 to S194 in FIG.63.

(Precedence of the Reverse Unidirectional Direction)

In the fourth embodiment described above, FIG. 63 is cited as anoperation example of the reference direction motion information decisionunit 161, but it is only necessary that unidirectional motioninformation should take precedence in the decision of motion informationand the present embodiment is not limited to such an example. Forexample, also in the decision of motion information in the reversedirection of the reverse direction motion information decision unit 162,like the reference direction motion information decision unit 161 in thefourth embodiment, unidirectional motion information may takeprecedence. In the decision of motion information in the reversedirection of the reverse direction motion information decision unit 162,like the reference direction motion information decision unit 161 in thefirst modification of the fourth embodiment, motion information may beselected by limiting to unidirectional motion information.

(Effect of the Fourth Embodiment)

In the fourth embodiment, by giving precedence to unidirectional motioninformation in the decision of motion information in the referencedirection, highly reliable motion information can be used as motioninformation in the reference direction and the encoding efficiency canbe improved by increasing the selection rate of a bidirectional combinedmotion information candidate.

Fifth Embodiment

(Deletion Process in Each Direction)

The configuration of a moving picture encoding device according to thefifth embodiment is the same as the configuration of the moving pictureencoding device 100 according to the first embodiment excluding thefunction of the combined motion information candidate generator 140.Hereinafter, a difference of the combined motion information candidategenerator 140 in the fifth embodiment from that in the first embodimentwill be described.

The configuration of the combined motion information candidate generator140 in the fifth embodiment from that in the first embodiment will bedescribed using FIG. 64. In FIG. 64, instead of the first combinedmotion information candidate list deletion unit 151 in FIG. 16, an L0direction motion information candidate list construction unit 155 and anL1 direction motion information candidate list construction unit 156 areprovided.

The function of the combined motion information candidate generator 140in the fifth embodiment will be described. If a plurality of combinedmotion information candidates having duplicate motion information in theL0 direction is present among motion information candidates contained inthe first combined motion information candidate list, the L0 directionmotion information candidate list construction unit 155 constructs an L0direction motion information candidate list by retaining one combinedmotion information candidate and supplies the L0 direction motioninformation candidate list to the bidirectional combined motioninformation candidate list construction unit 152.

If a plurality of combined motion information candidates havingduplicate motion information in the L1 direction is present among motioninformation candidates contained in the first combined motioninformation candidate list, the L1 direction motion informationcandidate list construction unit 156 constructs an L1 direction motioninformation candidate list by retaining one combined motion informationcandidate and supplies the L1 direction motion information candidatelist to the bidirectional combined motion information candidate listconstruction unit 152.

The bidirectional combined motion information candidate listconstruction unit 152 constructs a bidirectional combined motioninformation candidate list from an L0 direction motion informationcandidate list supplied by the L0 direction motion information candidatelist construction unit 155 and an L1 direction motion informationcandidate list supplied by the L1 direction motion information candidatelist construction unit 156.

The configuration of a moving picture decoding device according to thefifth embodiment is the same as the configuration of the moving picturedecoding device 200 according to the first embodiment excluding thefunction of the combined motion information candidate generator 140. Thecombined motion information candidate generator 140 of the movingpicture decoding device according to the fifth embodiment is the same asthe combined motion information candidate generator 140 of a movingpicture encoding device according to the fifth embodiment.

(Effect of the Fifth Embodiment)

In the fifth embodiment, generation of the same bidirectional combinedmotion information is inhibited by reducing redundancy of motioninformation in the L0 direction and the L1 direction and the encodingefficiency can be improved by increasing validity of a bidirectionalcombined motion information candidate.

Sixth Embodiment

(Selective Use of Bidirectional Combined Motion Information Candidates)

The configuration of a moving picture encoding device according to thesixth embodiment is the same as the configuration of the moving pictureencoding device 100 according to the first embodiment excluding thefunction of the reference direction decision unit 160. First, it isassumed that the candidate number management table in the sixthembodiment is given by FIG. 65 and the maximum number of combined motioninformation candidates contained in a combined motion informationcandidate list is 6. The sixth embodiment is different in that themaximum number of combined motion information candidates contained in acombined motion information candidate list is 6 and only one mergecandidate number is assigned to a bidirectional combined motioninformation candidate. Hereinafter, a difference of the referencedirection decision unit 160 in the sixth embodiment from that in thefirst embodiment will be described. The operation of the referencedirection decision unit 160 in the sixth embodiment will be describedusing FIG. 66.

The reference direction decision unit 160 repeats the followingprocessing as many times as the number (NCands) of combined motioninformation candidates contained in the second combined motioninformation candidate list (S300 to S305). The validity of the L0direction of a combined motion information candidate is inspected(S301). If the L0 direction of the combined motion information candidateis valid (YES in S301), the reference direction is set to L0 before theprocessing being terminated (S302). If the L0 direction of the combinedmotion information candidate is invalid (NO in S301), the validity ofthe L1 direction of the combined motion information candidate isinspected (S303). If the L1 direction of the combined motion informationcandidate is valid (YES in S303), the reference direction is set to L1before the processing being terminated (S304). If the L1 direction ofthe combined motion information candidate is invalid (NO in S303), thenext candidate is inspected (S305). If the reference direction cannot beset, no bidirectional combined motion information candidate will begenerated (S306).

The configuration of a moving picture decoding device according to thesixth embodiment is the same as the configuration of the moving picturedecoding device 200 according to the first embodiment excluding thefunction of the reference direction decision unit 160. The referencedirection decision unit 160 of the moving picture decoding device in thesixth embodiment is the same as the reference direction decision unit160 of a moving picture encoding device in the sixth embodiment.

(Effect of the Sixth Embodiment)

In the sixth embodiment, by determining whether to adopt the L0direction or the L1 direction as the reference direction depending onthe prediction direction of a combined motion information candidatecontained in the combined motion information candidate list, if only onebidirectional combined motion information candidate is valid, thevalidity of the bidirectional combined motion information candidate isincreased and selectivity of the bidirectional combined motioninformation candidate is increased so that the encoding efficiency canbe improved.

A bitstream of moving pictures output from a moving picture encodingdevice according to the first to sixth embodiments described above has aspecific data format so as to be decodable in accordance with theencoding method used in the first to sixth embodiments. A moving picturedecoding device corresponding to the moving picture encoding device candecode a bitstream in the specific data format.

More specifically, the merge index showing a bidirectional combinedmotion information candidate and a candidate number management table areencoded in a bitstream. A candidate number management table may not beencoded in a bitstream by encoding the merge index showing abidirectional combined motion information candidate and sharing thecandidate number management table between the moving picture encodingdevice and the moving picture decoding device.

When a wire or wireless network is used to exchange a bitstream betweenthe moving picture encoding device and the moving picture decodingdevice, the bitstream may be transmitted after being converted into adata format suitable for the transmission form of a communication path.In such a case, a moving picture transmission device that transmits abitstream output by the moving picture encoding device after thebitstream being converted into coding data in a data format suitable forthe transmission form of a communication path to a network and a movingpicture reception device that restores a bitstream after coding databeing received from the network and supplies the bitstream to the movingpicture decoding device.

The moving picture transmission device includes a memory that buffers abitstream output by the moving picture encoding device, a packetprocessing unit that packetizes a bitstream, and a transmission unitthat transmits packetized coding data via a network. The moving picturereception device includes a reception unit that receives packetizedcoding data via a network, a memory that buffers the received codingdata, and a packet processing unit that that generates a bitstream byperforming a packet processing of coding data and provides the bitstreamto the moving picture decoding device.

The above processing of encoding and decoding can naturally be realizednot only as transmission, accumulation, and reception devices usinghardware, but also by firmware stored in ROM (TRead Only Memory) orflash memory or software of a computer or the like. The firmware programor software program can be provided by recording in a computer readablerecording medium, from a server through a wire or wireless network, oras data broadcasting of terrestrial or satellite digital broadcasting.

In the foregoing, the present invention has been described based on itsembodiments. Those skilled in the art understand that such embodimentsare illustrative and combinations of each element and each processthereof can be modified and such modifications are also included in thescope of the present invention.

Subsequently, the operation of constructing a temporal combined motioninformation candidate list has been described using the flow chart inFIG. 26. The flow chart includes processing to calculate a motion vectorof a temporal combined motion information candidate (S164). For thetemporal combined motion information candidate, bidirectional motioninformation is calculated in reference to a reference picture ColRefPicand a motion vector mvCol in the prediction direction valid in motioninformation of the candidate block. If the prediction direction of thecandidate block is unidirectional (the L0 direction of the L1direction), a reference picture and a motion vector in the predictiondirection are selected as a reference. If the prediction direction ofthe candidate block is bidirectional, a reference picture and a motionvector in one of the L0 direction and the L1 direction are selected as areference. After the reference picture and the motion vector to be areference for generating bidirectional motion information are selected,a motion vector of the temporal combined motion information candidate iscalculated.

A technique of calculating motion vectors mvL0t, mvL1t of temporalcombined motion information candidates from the motion vector ColMv andthe reference picture ColRefPic as a reference for generatingbidirectional motion information will be described using FIG. 67.

If the distance between pictures ColPic and ColRefPic is ColDist, thedistance between the reference picture ColL0Pic in the L0 direction of atemporal combined motion information candidate and a processing targetpicture CurPic is CurL0Dist, and the distance between the referencepicture ColL0Pic in the L1 direction of the temporal combined motioninformation candidate and the processing target picture CurPic isCurL1Dist, the motion vector in Formula 1 below obtained by scalingColMv in the distance ratio of ColDist to CurL0Dist, CurL0Dist is set asthe motion vector of the temporal combined motion information candidate.The distance between pictures is calculated using POC and has a positiveor negative sign.

mvL0t=mvCol×CurrL0Dist/ColDist

mvL1t=mvCol×CurrL1Dist/ColDist  (Formula 1)

ColPic, ColRefPic, ColL0Pic, and ColL0Pic in FIG. 67 are only an exampleand other relationships may also be adopted.

[Item 1]

A picture encoding device with a motion compensation predictioncomprising:

a candidate list construction unit configured to select a plurality ofblocks each having one or two pieces of motion information containing atleast information about a motion vector and information about areference picture from a plurality of neighboring encoded blocks of anencoding target block and to construct a candidate list containingcandidates of the motion information used for the motion compensationprediction from the motion information of the selected blocks;

a first motion information deriving unit configured to derive the motioninformation of a first prediction list from a first candidate containedin the candidates;

a second motion information deriving unit configured to derive themotion information of a second prediction list from a second candidatecontained in the candidates; and

a selected candidate generator configured to generate a new candidate ofthe motion information by combining the motion information of the firstprediction list derived by the first motion information deriving unitand the motion information of the second prediction list derived by thesecond motion information deriving unit.

[Item 2]

The picture encoding device according to item 1, wherein

when a number of the candidates does not reach a set maximum number, thecandidate list construction unit constructs a candidate list including anew candidate generated by the selected candidate generator.

[Item 3]

The picture encoding device according to item 2, wherein the candidatelist construction unit constructs the candidate list including at leastthe one candidate generated by the selected candidate generator suchthat the number of the candidates does not exceed the maximum number.

[Item 4]

The picture encoding device according to any of items 1 to 3, furtherincluding:

a bitstream generator configured to encode candidate identificationinformation to identify the candidate of the motion information used forthe motion compensation prediction in the candidate list.

[Item 5]

The picture encoding device according to item 4, wherein

the candidate list construction unit assigns the candidateidentification information larger than that of the candidates to the newcandidate generated by the selected candidate generator.

[Item 6]

The picture encoding device according to any of items 1 to 5, wherein

the first prediction list and the second prediction list are differentprediction lists.

[Item 7]

The picture encoding device according to any of items 1 to 6, wherein

the candidate list construction unit includes the motion informationderived from the motion information of the block of a picture temporallydifferent from the picture including the encoding target block in thecandidate list.

[Item 8]

The picture encoding device according to any of items 1 to 7, wherein

the first motion information deriving unit searches the candidatesaccording to a first priority order for the candidate that becomes validto set the candidate as the first candidate, and

the second motion information deriving unit searches the candidatesaccording to a second priority order for the candidate that becomesvalid to set the candidate as the second candidate.

[Item 9]

The picture encoding device according to any of items 1 to 7, wherein

the first motion information deriving unit sets a preset candidate amongthe candidates as the first candidate, and

the second motion information deriving unit sets another presetcandidate among the candidates as the second candidate.

[Item 10]

The picture encoding device according to any of items 1 to 9, wherein

when both of the motion information of the first prediction list and themotion information of the second prediction list derived by the firstmotion information deriving unit and the second motion informationderiving unit respectively are valid, the selected candidate generatorgenerates the new candidate.

[Item 11]

The picture encoding device according to any of items 1 to 10, wherein

the new candidate holds two pieces of the motion information.

[Item 12]

The picture encoding device according to any of items 1 to 9, wherein

the new candidate holds one piece of the motion information.

[Item 13]

A picture encoding method with a motion compensation predictioncomprising:

selecting a plurality of blocks each having one or two pieces of motioninformation containing at least information about a motion vector andinformation about a reference picture from a plurality of neighboringencoded blocks of an encoding target block and constructing a candidatelist containing candidates of the motion information used for the motioncompensation prediction from the motion information of the selectedblocks;

deriving the motion information of a first prediction list from a firstcandidate contained in the candidates;

deriving the motion information of a second prediction list from asecond candidate contained in the candidates; and

generating a new candidate of the motion information by combining themotion information of the first prediction list and the motioninformation of the second prediction list.

[Item 14]

A picture encoding program with a motion compensation prediction,

the program causing a computer to execute:

selecting a plurality of blocks each having one or two pieces of motioninformation containing at least information about a motion vector andinformation about a reference picture from a plurality of neighboringencoded blocks of an encoding target block and constructing a candidatelist containing candidates of the motion information used for the motioncompensation prediction from the motion information of the selectedblocks;

deriving the motion information of a first prediction list from a firstcandidate contained in the candidates;

deriving the motion information of a second prediction list from asecond candidate contained in the candidates; and

generating a new candidate of the motion information by combining themotion information of the first prediction list and the motioninformation of the second prediction list.

[Item 15]

A picture decoding device with a motion compensation predictioncomprising:

a candidate list construction unit configured to select a plurality ofblocks each having one or two pieces of motion information containing atleast information about a motion vector and information about areference picture from a plurality of neighboring decoded blocks of adecoding target block and to construct a candidate list containingcandidates of the motion information used for the motion compensationprediction from the motion information of the selected blocks;

a first motion information deriving unit configured to derive the motioninformation of a first prediction list from the first candidatecontained in the candidates;

a second motion information deriving unit configured to derive themotion information of a second prediction list from a second candidatecontained in the candidates; and

a selected candidate generator configured to generate a new candidate ofthe motion information by combining the motion information of the firstprediction list derived by the first motion information deriving unitand the motion information of the second prediction list derived by thesecond motion information deriving unit.

[Item 16]

The picture decoding device according to item 15, wherein

when a number of the candidates does not reach a set maximum number, thecandidate list construction unit constructs a candidate list including anew candidate generated by the selected candidate generator.

[Item 17]

The picture decoding device according to item 16, wherein

the candidate list construction unit constructs the candidate listincluding at least the one candidate generated by the selected candidategenerator such that the number of the candidates does not exceed themaximum number.

[Item 18]

The picture decoding device according to any of items 15 to 17, furthercomprising:

a bitstream analysis unit configured to decode candidate identificationinformation to identify the candidate of the motion information used forthe motion compensation prediction in the candidate list, and

a selection unit configured to select one candidate from the candidatescontained in the candidate list by using the decoded candidateidentification information.

[Item 19]

The picture decoding device according to item 18, wherein

the candidate list construction unit assigns the candidateidentification information larger than that of the candidates to the newcandidate generated by the selected candidate generator.

[Item 20]

The picture decoding device according to any of items 15 to 19, wherein

the first prediction list and the second prediction list are differentprediction lists.

[Item 21]

The picture decoding device according to any of items 15 to 20, wherein

the candidate list construction unit includes the motion informationderived from the motion information of the block of a picture temporallydifferent from the picture including the decoding target block in thecandidate list.

[Item 22]

The picture decoding device according to any of items 15 to 21, wherein

the first motion information deriving unit searches the candidatesaccording to a first priority order for the candidate that becomes validto set the candidate as the first candidate, and

the second motion information deriving unit searches the candidatesaccording to a second priority order for the candidate that becomesvalid to set the candidate as the second candidate.

[Item 23]

The picture decoding device according to any of items 15 to 21, wherein

the first motion information deriving unit sets a preset candidate amongthe candidates as the first candidate, and

the second motion information deriving unit sets another presetcandidate among the candidates as the second candidate.

[Item 24]

The picture encoding device according to any of items 15 to 23, wherein

when both of the motion information of the first prediction list and themotion information of the second prediction list derived by the firstmotion information deriving unit and the second motion informationderiving unit respectively are valid, the selected candidate generatorgenerates the new candidate.

[Item 25]

The picture decoding device according to any of items 15 to 24, wherein

the new candidate holds two pieces of the motion information.

[Item 26]

The picture decoding device according to any of items 15 to 23, wherein

the new candidate holds one piece of the motion information.

[Item 27]

A picture decoding method with a motion compensation predictioncomprising:

selecting a plurality of blocks each having one or two pieces of motioninformation containing at least information about a motion vector andinformation about a reference picture from a plurality of neighboringdecoded blocks of a decoding target block and constructing a candidatelist containing candidates of the motion information used for the motioncompensation prediction from the motion information of the selectedblocks;

deriving the motion information of a first prediction list from a firstcandidate contained in the candidates;

deriving the motion information of a second prediction list from asecond candidate contained in the candidates; and

generating a new candidate of the motion information by combining themotion information of the first prediction list and the motioninformation of the second prediction list.

[Item 28]

A picture decoding program with a motion compensation prediction,

the program causing a computer to execute:

selecting a plurality of blocks each having one or two pieces of motioninformation containing at least information about a motion vector andinformation about a reference picture from a plurality of neighboringdecoded blocks of a decoding target block and constructing a candidatelist containing candidates of the motion information used for the motioncompensation prediction from the motion information of the selectedblocks;

deriving the motion information of a first prediction list from a firstcandidate contained in the candidates;

deriving the motion information of a second prediction list from asecond candidate contained in the candidates; and

generating a new candidate of the motion information by combining themotion information of the first prediction list and the motioninformation of the second prediction list.

What is claimed is:
 1. A picture decoding device with a motioncompensation prediction comprising: a candidate list construction unitconfigured to select a plurality of blocks each having one or two piecesof motion information containing at least information about a motionvector and information about a reference picture from a plurality ofneighboring decoded blocks of a decoding target block and to construct acandidate list containing candidates of the motion information used forthe motion compensation prediction from the motion information of theselected blocks; a first motion information deriving unit configured toderive from a first candidate contained in the candidates first motioninformation in a first direction; a second motion information derivingunit configured to derive from a second candidate different from thefirst candidate contained in the candidates second information in asecond direction different from the first direction; and a selectedcandidate generator configured to generate a first new candidate of themotion information by combining the first motion information and thesecond motion information, wherein the first motion information derivingunit further derives from the second candidate third motion informationin the first direction, the second motion information deriving unitfurther derives from the first candidate fourth motion information inthe second direction, the selected candidate generator generates asecond new candidate of the motion information by combining the thirdmotion information and the fourth motion information, and the candidatelist construction unit constructs the candidate list including at leastone new candidate generated by the selected candidate generator suchthat the number of the candidates does not exceed a set maximum number.2. A picture decoding method with a motion compensation predictioncomprising: selecting a plurality of blocks each having one or twopieces of motion information containing at least information about amotion vector and information about a reference picture from a pluralityof neighboring decoded blocks of a decoding target block andconstructing a candidate list containing candidates of the motioninformation used for the motion compensation prediction from the motioninformation of the selected blocks; deriving from a first candidatecontained in the candidates first motion information in a firstdirection; deriving from a second candidate different from the firstcandidate contained in the candidates second motion information in asecond direction different from the first direction; generating a firstnew candidate of the motion information by combining the first motioninformation and the second motion information; deriving from the secondcandidate third motion information in the first direction; deriving fromthe first candidate fourth motion information in the second direction;and generating a second new candidate of the motion information bycombining the third motion information and the fourth motioninformation; wherein the constructing a candidate list constructs thecandidate list including at least one new candidate generated by thegenerating the first/second new candidate such that the number of thecandidates does not exceed a set maximum number.
 3. A non-transitorycomputer-readable recording medium having embedded thereon a picturedecoding program with a motion compensation prediction, the picturedecoding program causing a computer to execute: selecting a plurality ofblocks each having one or two pieces of motion information containing atleast information about a motion vector and information about areference picture from a plurality of neighboring decoded blocks of adecoding target block and constructing a candidate list containingcandidates of the motion information used for the motion compensationprediction from the motion information of the selected blocks; derivingfrom a first candidate contained in the candidates first motioninformation in a first direction; deriving from a second candidatedifferent from the first candidate contained in the candidates secondmotion information in a second direction different from the firstdirection; generating a first new candidate of the motion information bycombining the first motion information and the second motioninformation; deriving from the second candidate third motion informationin the first direction; deriving from the first candidate fourth motioninformation in the second direction; and generating a second newcandidate of the motion information by combining the third motioninformation and the fourth motion information; wherein the constructinga candidate list constructs the candidate list including at least onenew candidate generated by the generating the first/second new candidatesuch that the number of the candidates does not exceed a set maximumnumber.